Anaphylaxis Is Probably Not As Lethal As You Think It Is

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Much like the scarlet kingsnake pictured above, anaphylaxis is often mistaken for something that’s likely to kill you (in the kingsnake’s case, that would be the coral snake, that could both kill you by poisoning you and by causing a lethal allergic reaction). But anaphylaxis is actually very unlikely to kill you. The fact is, every few minutes, someone, somewhere is having an anaphylactic attack, which they are very probably not treating properly, and they will they still walk away from it. That’s not to say that anaphylactic reactions are not dangerous. They are. And they are especially dangerous for certain demographics. But, in the vast, vast majority of cases, they are not fatal, especially if you know what to do when you have one.

This page will answer the following questions:

What is anaphylaxis?

Your immune system is constantly on the look-out for antigens—like bacteria, viruses and fungi—to fight. When it comes across an antigen for the first time, it learns to recognise it and files the information away for future use.

Allergies happen when your immune system decides that an otherwise innocent substance like a food protein poses a risk to you and needs to be taken out. When it comes across that food protein again, it overreacts, producing way too many inflammatory chemicals like histamine that then go on to affect your body in a variety of ways and can quickly turn the situation into a medical emergency.

An allergic reaction can affect multiple organ systems:

• The skin; cutaneous symptoms include itchiness, rash, hives, swelling
• The airways; respiratory symptoms include persistent coughing, difficulty talking or swallowing, wheezing, bronchospasm
• The gastrointestinal system; GI symptoms include stomach pain, nausea, vomiting, diarrhoea
• The cardiovascular system; CV symptoms include pallor, rapid heartbeat, heart palpitations
• The nervous system; neurological symptoms include dizziness, confusion, a ‘feeling of impending doom’

Allergic reactions can be classified by degrees of severity, either 4 or 5 of them, depending on the grading system being used. There is no international standard for grading these reactions but, in 2021, a panel of American experts came up with a grading system designed to harmonise the various existing systems and guide the treatment of severe allergic reactions:

	Reaction type	Requirements	Symptom examples
Grade 1	Mild reaction	Any mild symptom	Skin/mucosal symptoms: localised hives or redness, facial swelling, runny nose GI symptoms: 1 or 2 episodes of vomiting or diarrhoea
Grade 2	Systemic reaction	2 or more mild symptoms OR any moderate symptom	Skin/mucosal symptoms: (mild = above) moderate = generalised hives, skin reddening, more severe facial/throat swelling GI symptoms: (mild = above) moderate = over 3 episodes of vomiting or diarrhoea
Grade 3	Moderate reaction	Any mild symptom	Respiratory symptoms: shortness of breath, chest tightness, coughing, mild wheezing CV symptoms: weak, dizzy, heart palpitations (infants: unexplained rapid heartbeat) Neurological symptoms: confusion, drowsiness (infants: unexplained irritability, decreased activity)
Grade 4	Severe reaction	Any moderate symptom OR severe mucosal symptom	Mucosal symptoms: severe tongue or throat swelling Respiratory symptoms: persistent coughing, difficulty breathing, moderate wheezing, harsh sound or high-pitched voice when breathing (stridor), low blood oxygen (may manifest as bluish skin/lips/nails) CV symptoms: low blood pressure which may manifest as rapid heartbeat and/or fainting (infants: mottled skin, bluish skin) Neurological symptoms: lack of alertness (infant: lethargy)
Grade 5	Medical emergency	Any severe symptom	Respiratory symptoms: cannot breathe without making an obvious effort (e.g. muscles around neck/shoulder work hard, nostrils flare, there is severe wheezing and/or grunting), stop breathing CV symptoms: anaphylactic shock, heart stops beating Neurological symptoms: lack of alertness, seizures (infants: floppiness)

At the mildest end of the spectrum, an allergic reaction is localised, which means that it is limited to the site that came into contact with the allergen. For example, when someone who is allergic to a fruit gets an itchy mouth and throat after eating that fruit, or the sneezing, runny nose and itchy eyes experienced by someone with hay fever.

A more serious type of allergic reaction is a systemic reaction. This type of reaction is a widespread reaction that affects areas of the body that did not come into direct contact with the allergen. For example, having a case of full-body hives after eating a trigger food. The reaction is considered more serious if it affects 2 or more organ systems or if the symptoms themselves are serious (e.g. difficulty breathing).

Anaphylaxis is the most severe type of systemic allergic reaction. Most medical organisations consider a Grade 3 reaction (see table) and above as anaphylaxis. It generally affects several organ systems or one organ system severely—e.g. a person’s tongue swells up to such an extent that they can’t breathe—and it has the potential to escalate fast into a medical emergency. But anaphylaxis does not necessarily start off as a medical emergency and it will often not become life-threatening.

Anaphylaxis is not what most people think it is. What most people are thinking of when they think of anaphylaxis is anaphylactic shock, which is when a massive drop in blood pressure causes someone to lose consciousness and/or a narrowing of their airways makes it impossible impossible for them to get in enough oxygen. Although an episode of anaphylaxis rarely ever gets this far, it’s impossible to tell whether or not it will, which is why each episode must be treated as if it will become life-threatening and adrenaline (if available) must be used!

You can read more about when an allergic reaction becomes anaphylaxis and how it treat it here.

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How common is anaphylaxis?

Anaphylaxis is thought to affect somewhere between 0.3 and 5.1% of the general population at some point in their lives, with 50 to 112 episodes occurring per 100,000 persons per year. An analysis of 12 years worth of European anaphylaxis data has produced anincidence rate for all-cause anaphylaxis ranging from 1.5 to 7.9 per 100 000 person-years, meaning that around 0.3% of the European population will experience anaphylaxis at some point in their lives. A 2023 global review of all-cause anaphylaxis put the number of anaphylactic episodes a year at around 46 cases per 100,000 individuals.

Not all cases of anaphylaxis are life-threatening, in fact few are, so when it comes to the most severe cases of anaphylaxis, the numbers are lower. A 2005 review of life-threatening and lethal anaphylaxis noted an incidence of severe anaphylaxis of 1 to 3 cases per 10,000 people and the incidence of lethal anaphylaxis at 1 to 3 per 1,000,000 people per year. A review published 10 years later calculated an incidence of lethal anaphylaxis at least 3 times smaller: 0.12 to 1.06 deaths per million person-years.

These data come with caveats because they are based on studies that are not entirely comparable, resulting in aggregate data that are ‘sparse and imprecise’ and lead to estimates of the frequency of anaphylaxis as vague as ‘approximately 50 to 2,000 episodes per 100,000 persons’.

The fact is, it’s difficult to calculate the number of people who may be affected by anaphylaxis. For a start, there are different definitions of anaphylaxis floating around, although the medical profession has been moving towards a consensus in recent years. However, researchers will have used different criteria in their studies, with more stringent definitions producing smaller numbers; for example, in a questionnaire study carried out in the US, when the criterion for a diagnosis of anaphylaxis was the involvement of 2 or more organ systems, together with respiratory or cardiovascular involvement, this produced a prevalence of 5.1% of anaphylaxis in the general population, but when the criteria included a hospital visit and threat to the patient’s life, the prevalence was 1.6%.

Researchers also collect their data in different ways, such as using codes entered in hospital data systems, or reports from allergy clinics, or questionnaires administered to the general public. As such, numbers can vary enormously; for example, estimates of the proportion of food-triggered allergic reactions that result in anaphylaxis range between 0.4% and 39.9%,

Additionally, anaphylaxis is notoriously ‘underdiagnosed, underreported, and undertreated’. Many of these studies depend on doctors coming up with the right diagnosis and entering the right codes into healthcare systems—it’s not uncommon, for example, for cases of anaphylaxis to be mislabelled as asthmatic reactions.

Then, there are different incidence rates in different countries. For example, the 2023 review calculated rates of, per 100,000 population per year, 8 cases for Asia, 17 cases for Australia, 43 cases for North America and 71 cases for Europe. This could be due to different definitions of anaphylaxis being used in different countries and/or because people in the different countries behave differently; a 2005 review found that 29 to 41% of the patients in ‘Anglo-Saxon countries‘ who showed up to a hospital’s emergency department were found to be experiencing severe anaphylaxis, whereas that number was only 3.7 to 8% when it came to French and Italian patients.

Which brings us to another point regarding these numbers; the vast majority of anaphylaxis studies are based on people visiting allergy clinics or hospital emergency rooms, not the numbers of people in the community who have an anaphylactic reaction but didn’t seek medical help—which may well be the majority of people—or those who visited their GP. So, the numbers regarding the prevalence of anaphylactic attacks in the general population are likely to be overestimates.

Helping to illustrate the point, a British study published in 2004 that was based on a national database of GP practice data calculated that just over 8 in 100,000 people could be expected to experience anaphylaxis every year, which is a lot smaller than the number suggested by most of the European studies using hospital-based data.

Finally, the number of people who are likely to experience anaphylaxis depends on the population under study. For example, children are more likely to experience anaphylaxis to food than adults, who are more likely to experience severe anaphylaxis to any trigger than children, someone who is allergic to food is more likely to experience anaphylaxis than someone who is allergic to venom, but the latter is more at risk of a life-threatening reaction, and people who live in areas of low sunlight are more likely to have an anaphylactic reaction than people who live in sunnier regions. Possibly.

One thing that most reviewers can agree on is that cases of all-cause anaphylaxis are on the increase (although this increase is not the same ‘for all causes or for all ages or for different causes of anaphylaxis in different age groups’); increases in hospital admissions for anaphylaxis have been reported since the 1990s and have come from all corners of the world, including Europe, various states in the US, and various countries in Australasia—such as Korea, Thailand, Australia and New Zealand— with studies reporting increases in numbers that range from 5-fold to 20-fold, mostly driven by medication- and food-related anaphylaxis.

Experts think that this increase is probably due to a combination of factors including the more frequent use of allergens in processed foods and non-food products, more people adopting a Western diet and/or suffering from stress which can damage our gut lining and lead to food allergies, increases in drug prescriptions and medical procedures that involve X-rays and the improved recognition of allergic reactions. As well as other factors we don’t even know about yet.

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How dangerous is anaphylaxis?

The World Allergy Organisation’s definition of anaphylaxis states that it is ‘potentially’ life-threatening. Because, although anaphylaxis can be dangerous, it’s highly unlikely to kill you.

A 2022 review of global data calculated that the figure for fatal anaphylaxis lies between 0.002 to 2.51 deaths per million person-years—which means that, taking the lowest estimate, if you followed 1 billion people for 1 year, 2 would die or, at the highest estimate, if you followed 2 million people for 1 year, 5 would die.

Anaphylactic attacks rarely ever result in hospitalisation, let alone death. A 2014 American study comfortingly titled ‘Death From Anaphylaxis Is a Reassuringly Unusual Outcome’ noted that between 0.25% and 0.33% of people who visit a hospital’s emergency department or are hospitalised because of an anaphylactic reaction end up dying, with over three quarters of those deaths occurring in people who had been hospitalised.

Using death certificate data from several different sources, they calculated an anaphylaxis-induced death rate of between 0.63 and 0.76 per million person-years, the equivalent of between 186 to 225 deaths per year among the American population, which was around 319 million people at the time.

Over the years, researchers have calculated death rate figures for the populations of several countries and, although they inevitably differ, they are fairly similar and none exceeds 1 person per million.

Researchers have calculated the lowest death rate for the UK—0.46 per million person-years (i.e. just under 1 death per 2 million people a year)—and the highest for Australia—0.99 per million person-years (i.e. just under 1 death per million people a year)—although a separate Australian study calculated a rate of 0.64 anaphylaxis deaths per million population per year, which is very close to the rates calculated for most other countries, including Finland (0.59 per million person-years), France (5) (0.6 per million person-years) and Italy (0.51 per million population per year), with Brazilian researchers calculating a slightly higher rate of 0.87 per million per year. On the whole, then, you could expect to see around 3 deaths due to anaphylaxis per every 5 million people in an average population per year.

Some triggers are more dangerous (i.e. more powerful and/or more common) than others and therefore come with a different level of risk; researchers estimate a mortality rate for food-induced anaphylaxis of 3 to 32 per 100 million people per year, a mortality rate for drug-induced anaphylaxis of 5 to 51 per 100 million people per year, and a mortality rate for venom-induced anaphylaxis of 9 to 13 per 100 million people per year.

The risk of dying from anaphylaxis also depends on the characteristics of the population being studied; for example, older people run a higher risk of dying from anaphylaxis than younger people, and are more likely to have a reaction to a different trigger, as shown by data from the UK fatal anaphylaxis register, the longest-running record of fatal anaphylaxis data, which has recorded around 1 anaphylactic death per 3 million of the UK population every year since 1992, and shows that about half of these were due to medication, mostly affecting older people, and the rest were due to sting reactions and food, the latter of which mostly affected younger people.

The good news is that, even though cases of anaphylaxis seem to be on the rise all around the world, researchers in several countries have not found a corresponding increase in the number of deaths caused by to anaphylaxis. In the UK, for example, a 2014 study noted an increase in anaphylaxis-related hospitalisations but no increase in fatalities. A 2017 study from France even found a slight decrease in the total number of deaths due to anaphylaxis, driven by a large fall in deaths due to drug-induced anaphylaxis.

A 2020 analysis of the global trends of anaphylaxis reported that, although the frequency of hospital admissions due to anaphylaxis has increased between 5- to 7-fold in the last 10 to 15 years, the number of deaths from anaphylaxis remained at the very low rate of 0.35 to 1.06 deaths per million people per year, with no observed increase over the last 10 to 15 years.

This is particularly striking considering the fact that the vast majority of reactions are not treated properly (that is, with the prompt administration of adrenaline*).

*Sidebar: Adrenaline or epinephrine? Adrenaline and epinephrine are generally used to describe the same thing. Epinephrine is the term used in America, Canada, Japan and Spain, and adrenaline is the preferred term pretty much everywhere else. For an argument on why adrenaline is considered the ‘more correct’ terminology, go here.

A few countries, however, have noted an increase in anaphylaxis-related deaths. For example, in Finland, there has been a steady increase in numbers over recent years, although those numbers (at the last count) were still in the single digits (and did not include any children).

The increase in total numbers is often driven by relatively large increases in deaths to specific triggers. For example, studies from the US and Canada have noted either stable or decreasing numbers of food-induced fatalities while simultaneously finding increases in drug-induced fatalities.

However, the picture can change over time. In Australia, a 2008 study found no increase in the rate of total fatalities to food, but reported a 3-fold increase in drug-related fatalities. But a subsequent study analysing government hospital and death registry datasets found a near doubling of fatalities between 1997 and 2013, driven in large part by reactions to food.

These numbers are not perfect; they rely on diagnoses and autopsy results that sometimes, for example, confuse asthma or heart failure with anaphylaxis as the cause of death, resulting in an underestimate of fatalities due to anaphylaxis. But at the same time, since many people do not seek medical help during or after an allergic reaction, the number of fatalities as a proportion of all anaphylactic cases is probably an overestimation.

What we can take from all of this, however, is that the vast, vast majority of people with allergies will not die as a result of an anaphylactic reaction.

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What are the most dangerous triggers?

The most dangerous triggers of anaphylaxis depend on your age, culture and geography. The most common triggers of IgE-mediated anaphylaxis worldwide are food, venom and medications, and they tend to cause severe reactions after being injected, ingested or absorbed through the skin.

Other less common triggers include cleaning detergents, environmental allergens—like grass or cereal pollens—and latex.

Latex is most likely to pose a risk for the latex-allergic in a medical context, generally during operations, but it can be hazardous outside of the healthcare environment by, for example, causing cross-reactions with certain fruits and vegetables including avocado, banana, chestnut and kiwi (also known as as latex-food syndrome) and primary reactions to everyday items like rubber gloves, sports equipment and party balloons as well as less commonplace items like calculator buttons and hair glue. On extremely rare occasions, the reaction can be fatal.

Some things—e.g. exercise, radiocontrast media, opioids and cold exposure—can trigger anaphylaxis without involving the immune system. This is a relatively rare way to trigger a reaction which will not be dealt with on this page.

Ultimately, the triggers most likely to cause severe reactions in people with allergies are the most common: food, medications and venom.

Food is a common trigger of anaphylaxis, but it’s generally considered the least likely to cause a severe reaction

Since the 1990s, food has been shown to be one of the most common anaphylaxis triggers. It’s the most common in the paediatric population, which probably explains why it’s also the most talked-about cause of anaphylaxis.

However, while food is the most common cause of anaphylaxis in the community (i.e. not treated by health professionals) and of hospital admissions due to anaphylaxis, it is much less likely to be the cause of severe reactions or fatalities than other triggers.

Considering the relatively large proportion of allergic people with a food allergy, the number who are severely affected by that food allergy is much smaller than you might think. For example, over a period of 3 years, the Allergy Vigilance Network, which collects data from hundreds of allergists in France and Belgium, recorded 229 cases of severe food-mediated anaphylaxis, 4 (2%) of which (in 2 children and 2 adults) proved to be fatal—which is the highest reported fatality rate among all the comparable studies.

Studies carried out in Finland, the US and Australia have found that food was responsible for 9%, 6% and 7% of all the anaphylaxis fatalities, respectively.

According to a 2022 analysis of international fatal anaphylaxis data, the chance of experiencing fatal food anaphylaxis lies between 0.002 to 0.29 deaths per million persons-years in the general population; which means that, if you followed a group of 1 billion people over the period of a year, you could expect between 2 and 290 of them to die from food-induced anaphylaxis.

In fact, death from food-related anaphylaxis is consistently lower than death from other causes across all regions of the world (although some countries, like France and Canada, do occasionally report a higher absolute number of fatalities linked to food).

A review of anaphylaxis data from several European countries, North America, Brazil, Israel and Australia calculated an estimated incidence of fatal food-induced anaphylaxis in a food-allergic individual of 1.81 per million person-years; thus, over the period of one year, in a population of 1 million (food-allergic) people, less than 2 individuals would be expected to die after having a severe reaction to their trigger food.

In fact, according to that study, the average food-allergic person in Europe or the US is less likely to die from food-induced anaphylaxis than they are from a random accident or murder.

Peanuts and tree nuts are a dangerous food trigger for people of all ages in many Western countries, being more frequently associated with very severe reactions, adrenaline treatment and hospitalisation than other foods, as well as being the leading cause of food-induced fatalities in Europe, Canada, the US, Australia and New Zealand.

This may be due to the fact that peanuts (and tree nuts) are more likely to cause allergies and severe reactions than other foods.

However, the most important food allergens in a population vary according to age and culinary tradition.

So, while peanuts and tree nuts may affect older children and adults in many populations, young children (generally, preschool-age children, often under the age of 2) are more likely to have severe reactions to milk, something that has been highlighted in a range of countries including France, Portugal, North America, China and Korea.

In the UK and Ireland, milk is now the most common cause of fatal anaphylaxis in children under 16 years old, and milk has also been found to be the most common cause of child fatalities in Israel.

This may be due to the fact that milk has a relatively high protein content, meaning that reactions can be caused by very low levels of exposure, which is relatively easy to achieve because milk is omnipresent in our foods and responsible for high rates of cross-contamination in products like baked goods.

In Australasia, seafood is a popular staple and people in that area of the world are more likely to have problems with seafood. In Australia and New Zealand, seafood (namely prawn/shrimp) is a common trigger for anaphylaxis, including in children—although peanuts are still the most common cause of death in that age group, whereas seafood tends to cause the most severe reactions in adults.

Likewise, seafood is a common cause of anaphylaxis in countries like China (Hong Kong) and Singapore, where the importance of cultural habits is highlighted by the fact that people with Eurasian backgrounds who live in Singapore are more likely to have problems with peanuts whereas the seafood anaphylaxis numbers are driven by people of Indian descent.

All of which does not mean that seafood—specifically, shellfish—allergy is not a problem in Western countries; in Europe, crustaceans tend to be an important trigger of anaphylaxis in school-age children and adolescents in seafood-loving countries like Portugal, and crustaceans (and milk) have both been reported to cause a higher proportion of anaphylaxis in adults than would be expected given the number of people who are reported to be allergic to those triggers. In Canada, food is a common trigger of anaphylaxis among adults and reactions to shellfish have been found to be more severe than reactions to other foods.

In the US (and in many other countries), seafood is the most common trigger of food-induced anaphylaxis among adults. At a national level, crustaceans are the third most common cause of anaphylaxis among children after peanuts and tree nuts. However, showing the importance of cultural eating habits, crustaceans are the most common trigger of anaphylaxis among children living in Southern states and one of the top 2 (the other being milk) in Midwestern children.

Similarly, a study of anaphylaxis admissions to paediatric intensive care units in North America revealed that the most common food triggers differed according to ethnicity; among black children, fish and crustaceans were the most common triggers, among Asian children, it was eggs and nuts, among Hispanic children, it was crustaceans, fish and eggs, and among white children, it was nuts and milk.

Seafood may be a particularly hazardous allergen in regions where it is popular not only because of the relatively high rates of consumptions and allergy in those areas but also because of the difficulty in distinguishing between seafood allergy and poisoning, which might stop people from seeking help from an allergist after an allergic reaction that looks like a bad case of stomach upset. Seafood also tends to provoke a reaction only after a relatively large amount has been eaten, meaning that some people may react when eating some seafood-containing dishes but not when consuming others, which could either mask an allergy or lead some people with a known seafood allergy to take more risks with the food that they try.

Other food triggers to watch out for in certain regions of the world include sesame in the Middle East, where it is sometimes referred to as ‘the Middle Eastern peanut‘, wheat in China, which accounts for a disproportionate number of cases of anaphylaxis in teenagers and adults, and wheat and buckwheat in Korea, which are major causes of anaphylactic reactions in children.

Wheat is also an important trigger of anaphylaxis in European adults, often in combination with exercise. In central European countries, wheat is actually the most common trigger for the most severe forms of anaphylaxis.

Pollen allergy plays an important role when it comes to food allergy in teenagers and adults, as it can lead to the development of pollen food syndrome (PFS), and is responsible for the relatively high prevalence of sometimes severe allergy to fruit and vegetables like celery and soy in adults.

PFS provokes symptoms of varying severity to plant food, depending on which pollen you’re sensitised to. In northern Europe, for example, allergies to hazelnut and certain fruits tend to cause fewer cases of anaphylaxis than they do in other regions of the world because the allergies in that region are often associated with birch pollen sensitisation, which often—but not always—provokes milder symptoms of allergy. In southern European countries, PFS is more likely to be linked to a sensitisation to pollens like mugwort, which tends to be associated another type of protein—lipid transfer protein (LTP)—which generally causes more severe reactions and is often associated with cofactors like exercise.

Another food that is more likely to affect adults than children is red (mammalian) meat—beef, pork or lamb—allergy, aka alpha-gal syndrome, which is becoming a more visible problem in any country where tick bites are a common problem. It was first brought to the world’s attention when people in the southern states of North America started suffering mysterious allergic reactions several hours after they ate red meat. Cases have now been reported on all 6 continents, notably in the southern, eastern and central United States and Australia, but also in other countries including the UK, Sweden, Germany, Poland, Italy, Japan and South Africa.

While people of all ages can develop an allergy to red meat, most cases have been reported in adults (though not in India) and cases of alpha-gal syndrome are reportedly on the rise, especially among among middle-aged and older adults. The first case of a fatal reaction to red meat (in a 47-year-old man) was reported in North America in 2025.

A person’s first allergic reaction to a food trigger occurs after they become sensitised to it. In the case of infants, this happens around the time a food is introduced into the diet; reactions to milk and eggs tend to occur before the age of 1, and reactions to other foods later. Often, a reaction happens the first time an infant eats a food, possibly because they have become sensitised to the proteins already via breast milk. Sometimes sensitisation happens via the skin, which is a relatively common way of becoming sensitised to peanut, especially when a child has eczema.

When a reaction to food is severe, it tends to involve the skin and the respiratory system. Fatal reactions normally involve difficulty breathing (aka dyspnoea) or asthma that, in most cases, leads to breathing stopping completely (respiratory arrest) around half an hour after eating the trigger food. People who die from food allergy have often had reactions before, but those have typically been mild.

Pro tip: When a food-allergic person suddenly has difficulty breathing after eating some food, the first treatment that should be considered is adrenaline (if there is an auto-injector available), before any other type of medication is used, even if that person has asthma. As a rule of thumb, a child who develops symptoms within 5 minutes of having eaten something should be considered at risk of having a severe reaction.

Different foods can provoke different symptoms; for example, wheat-induced anaphylaxis has been shown to be more frequently associated with cardiovascular symptoms and cashew-induced anaphylaxis with gastrointestinal symptoms, and milk and hazelnut tend to provoke a more severe type of anaphylaxis than cashew nuts, soy or celery.

Different foods also require different amounts to provoke symptoms; for example, nuts and peanuts seem to require the equivalent of 1 teaspoons or less, whereas egg and milk require up to one tablespoon or more, and wheat, shellfish and meat may only provoke symptoms after a full portion size is eaten. And food types can be surprising, with celeriac needing smaller amounts than nuts or peanuts to provoke a reaction.

Ultimately, everyone has their own individual way of reacting to food and their reactions can also vary in severity from episode to episode. This may be due to the fact that reactions to certain foods can be worsened by certain types of cofactor; for example, while wheat anaphylaxis is often associated with exercise, wheat anaphylaxis can be worsened by alcohol when it’s drunk together with a wheat-containing meal or within 1 hour before or after eating, and exercise can also worsen anaphylaxis to peanut.

Ultimately, all foods have the potential to cause severe reactions in people who are allergic to them; from seemingly innocuous foods like lettuce, to more ‘exotic’ foods like royal jelly, wild boar and additives like gum arabic.

Finally, the amount a person eats may also affect the seriousness of their reaction.

In a unique study, peanut-allergic children were given food challenges that were not terminated when mild symptoms were first spotted. Instead, the children were given more peanut to eat until the symptoms became more serious or they ate the maximum dose. 21 of the children ended up experiencing anaphylaxis. Crucially, anaphylaxis was not the initial symptom in the majority of the cases; ultimately, 13 children who started off with mild symptoms ended up experiencing anaphylaxis after eating more peanut. Furthermore, a history of anaphylaxis did not predict whether or not a child ended up experiencing anaphylaxis during this challenge.

This pattern has been reproduced in other studies, which experts think implies that food-allergic individuals have a threshold of reactivity for having any symptoms at all and a higher threshold for experiencing symptoms of anaphylaxis. In some people, those 2 thresholds may be so close that they will seem to experience anaphylaxis as their initial symptom, especially if they eat their food fast enough.

All of which implies that just because someone has not suffered anaphylaxis before does not mean that they are not at risk from suffering it in future; they may just not have eaten enough of their trigger food.

Food-induced anaphylaxis has been shown by various different studies to be on the increase, sometimes by quite a lot. A review of British medical data, for example, reported that hospital admissions for food-induced anaphylaxis had increased by 700% between 1990 and 2007, whereas a review of Australian anaphylaxis data reported that hospital admissions for food-induced anaphylaxis had increased by around 350%, driven mainly by anaphylaxis to peanuts (especially among 0- to 4-year-olds), crustaceans and milk.

However, fatalities as a result of food-induced anaphylaxis are not on the rise (one study from Australia reported that fatalities were on the increase, but another one did not, and one study from Canada even showed a decline). This could be due to increased awareness of food allergies and/or better treatment. Either way, it’s good news for the food-allergic.

Medications are the most common cause of (fatal) anaphylaxis in many countries

Drugs are the most commonly identified trigger of anaphylaxis in several countries around the world, including China, Korea, the Lebanon and the US, where an analysis of national healthcare records reported that, among the 1,756,481 patients included in the database, 622,152 (35.4%) reported at least one drug allergy and 19,836 (1.1%) had had at least one case of drug-induced anaphylaxis.

In Australia, drugs have been reported as the second most commonly identified trigger of anaphylaxis, and a study of Thai children also put it at number 2 in that age group. It has likewise been identified as the second most commonly identified trigger of anaphylaxis in Turkey and Poland, In Europe as a whole, drugs are the third most frequently reported cause of anaphylaxis.

Drugs are the most frequently reported cause of fatal anaphylaxis in several countries, representing at least half of all fatal cases of anaphylaxis in the UK, France, Italy, the US and New Zealand, mainly in older age groups. In Australia medications are the most common cause of death among the identified triggers. In Shanghai, drugs (namely antibiotics) were responsible for all 11 deaths reported in one study.

The symptoms of drug-induced anaphylaxis are often very severe and appear very quickly, often within 5 minutes (although they can take over 4 hours to appear). They tend to be more severe than reactions provoked by food, and often involve sudden cardiovascular collapse (severe dizziness, shortness of breath or unconsciousness as a result of the heart and blood vessels not maintaining adequate blood circulation to vital organs), especially in older patients.

Although a drug that is applied to the skin or injected is more likely to cause severe reactions than a drug that is swallowed, drugs taken orally can also provoked severe anaphylaxis. In fact, all routes of administration are potentially lethal. Doses of medication that are taken often, or high doses that are taken over a long period of time are more likely to lead to reactions than a large single dose.

Risk factors for severe drug-induced anaphylaxis are not consistent across studies. Some have found that being white and female are risk factors for more severe reactions to drugs, but others have found that being African American and male are risk factors for worse reactions.

Other studies have reported that being atopic—prone to allergies—having mastocytosis or pre-existing lung disease is a risk factor for more severe reactions to drugs, but some research has found that severe reactions to drugs is less likely if you have asthma.

The only risk factor that consistently comes up when it comes to severe allergic reactions to drugs is older age; adults are over five times more likely to suffer drug-induced anaphylactic attacks than children according to one European review. Although children can have reactions to drugs, medication as an anaphylactic trigger is more likely with increasing age, becoming a more important cause of reactions in teenagers.

Drug induced anaphylaxis is more likely to occur in adults as they head towards middle-age, with hospitalisations peaking in adults aged 55 and over. This is also the age when drug-induced reactions are more likely to be fatal, with studies finding that the death rate peaks over the age of 60, in the seventh decade of life, and affects both sexes equally. Fatalities in children are rare; one Australian study examining 15 years worth of data reported no drug-induced deaths in anyone under the age of 15.

Although triggers for drug-induced anaphylaxis will differ somewhat by country, a group of usual suspects tend to cause the most reactions.

Nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin and ibuprofen are frequently associated with anaphylactic reactions in both children and adults —especially as cofactors involved in reactions to food, where they are thought to enhance the absorption of food allergens in the gut. However, they generally (though not always) cause less severe reactions than other drugs and are involved in relatively few fatal reactions.

The drugs most often involved in severe and fatal reactions are antibiotics, like penicillin. Antibiotics have been mentioned as a leading cause of severe drug-induced anaphylaxis in children and adults in multiple countries from France and Turkey to the US and China, and as the leading cause of drug-induced fatal reactions in studies carried out in France, Turkey, the US, Canada, Australia and China, where they cause around 3 in 4 of drug-induced deaths.

Antibiotics feature so highly among drug-induced reactions because they are responsible for many of the anaphylactic episodes in medical settings, especially during operations, when they are responsible for a large number of the reactions experienced during anaesthesia (along with muscle relaxants and latex), often in patients who have no history of of drug-induced allergy nor indeed of any allergy. Fatalities, however, are extremely rare, with the risk of life-threatening reactions estimated to be around 1 in 10,000 operations.

Another class of drug that is associated with severe reactions are radiocontrast agents (aka contrast media)—substances like iodine that are used in medical imaging (like X-rays) to enhance the visibility of internal structures. Radiocontrast agents have been mentioned as the leading cause of drug-induced anaphylaxis in at least one study in Seoul, South Korea, and they were reported as the leading cause of fatal hospital-based reactions in Ontario, Canada. They also feature prominently in studies from Australia, China and the US, where one report found that radiocontrast agents presented a higher fatality risk ‘per injection’ than the more frequently used antibiotics. A separate study carried out by researchers based in Switzerland and Italy also pointed out that many of the fatalities to contrast media in their hospital network have occurred on first exposure.

Other medications that are mentioned in association with anaphylaxis include neuromuscular blocking agents, proton pump inhibitor (PPI) medication—which are also involved in reactions involving food as they make it more difficult for the digestive system to break down food allergens—β-blockers and ACE inhibitors (especially when used in combination), the anti-cancer medication cetuximab and, somewhat ironically, medication that is sometimes used to minimise the severity of allergic reactions, like omalizumab (brand name Xolair).

Ultimately, pretty much any medication has the potential to cause anaphylaxis and many can do this either by activating IgE antibodies or by activating mast cells directly without any involvement of the immune system.

An increase in hospitals admissions and deaths due to drug-induced anaphylaxis has been reported in various countries around the world. Some studies from the US and Australia have noted a significant increase in fatalities, with deaths in the US between 1999 and 2010 reportedly doubling (although a study examining anaphylaxis deaths between 1999 and 2006 shows a relatively stable rate, which increases only slightly over time) and deaths in Australia between between 1997 and 2005 reportedly tripling, (although another study reported an insignificant change in medication-related fatalities between 1997 and 2013 of 5.6%). By contrast, an analysis of fatal anaphylaxis data in the UK showed no increase in drug-induced fatalities, even though hospital admissions were up.

Where increases have been reported, researchers suspect that it may be due, at least in part, to an increase in prescriptions—of a wider variety of drugs—and medical procedures, especially those involving radiocontrast media which often cause reactions with first-time exposures.

Venom is actually the most dangerous trigger

Although cases of venom-induced anaphylaxis generally represent a small proportion of hospital admissions, insect venom is responsible for more fatalities than any other trigger, highlighting the seriousness of insect allergy.

The most common trigger of venom-induced anaphylaxis are stinging insects belonging to the Hymenoptera order, which includes bees, vespids (wasps, yellow jackets, hornets) and stinging ants. Hymenoptera (or insect) venom is mentioned as one of the top 3 triggers for anaphylaxis in most countries around the world.

Epidemiological studies have estimated that Hymenoptera stings are responsible for between 0.3 to 42.8% of anaphylaxis cases, with a death rate estimated at around 0.1 cases per million population (or 1 in 10 million inhabitants per year) in the UK, Australia, Canada and the US. In Europe, a recent review put the number of fatalities at 0 to 2.24 per million inhabitants per year, with an average of 0.26, with fatalities mostly occurring in Western (42.8%) and Eastern (31.9%) Europe.

The risk of being bitten depends on where you live, as does the source of the danger. In northern and central Europe, for example, wasps are the most common trigger for venom-induced anaphylaxis. And in France, you’re more likely to have a venom-induced reaction in the south of the country, where there are more bee hives and the climate ensures a longer exposure to venomous insects.

In the US, you’re also more likely to experience a severe or fatal venom-induced reaction in a southern state, rather than a northern one. In a similar vein, a 2003 study revealed that 17% of the residents of Augusta, Georgia were sensitised to fire ants, more than the number of people in the region who were sensitised to peanuts.

Fire ants are a particular problem in the southern states of the US (notably Florida and Texas as well as the Caribbean and parts of Asia and Australia. They are a common and aggressive pest, and they are becoming more of a problem for Europeans, who also have to deal with other stinging insects like horseflies.

In Australia, bees are actually the leading cause of hospital admissions and fatal reactions, probably because humans are more likely to come into contact with them than they are wasps, and they are also the main cause of venom-induced anaphylaxis cases in Turkey, where beekeeping is a common source of livelihood.

Insects do not have to be venomous to cause anaphylactic reactions; tick bites, for example, are a relatively common cause of anaphylaxis (apart from their association with alpha-gal—red meat—allergy) and caterpillar bites have also been known to cause severe reactions.

In the non-insect category, snake venom, as well as being poisonous, is also a potential cause of anaphylaxis, and the cure itself can be risky; the antivenom used for snake bites is itself a not uncommon cause of anaphylaxis. Even people who work on producing that antivenom are at risk of experiencing a serious reaction.

In fact, being bitten by anything can be hazardous, because people can be sensitised to proteins in the saliva of all kinds of animals like, for example, hamsters, who are also the subject of the occasional case report of anaphylaxis.

Although venom-induced anaphylaxis appears in early school-age, multiple studies investigating anaphylaxis have found that adults are at much greater risk of experiencing venom-induced anaphylaxis than children, with the demographic the most at risk of suffering a severe or fatal reaction being white, middle-aged males. Why this is the case is unknown, but it may have something to do with the types of (outdoor) jobs they are more likely to have.

Another potential risk factor for severe reactions to venom is heart disease, which is linked to older age and also associated with taking medication like angiotensin-converting enzyme (ACE) inhibitors, which have also been linked to a higher risk of more severe reactions to venom. Finally, systemic mastocytosis has also been reported as a potential risk factor for severe venom-induced anaphylaxis.

Venom-induced anaphylactic reactions generally occur during the summer months, when insects—the most common culprits—are out and about doing their thing. Numbers tend to peak when people stand the greatest chance of running into the most dangerous insects in the region—in the UK, for example, this is in August, when wasp populations are at their highest.

Symptoms typically appear within 10 minutes of being stung, with severe life-threatening reactions occurring within half an hour, often within 10 to 15 minutes after being stung or bitten.

Venom-induced reactions are often associated with the most severe type of anaphylaxis, and tend to be more severe than those caused by other triggers, with some stinging insects—like hornets—producing more serious reactions than others. Reactions to insect stings often involve cardiovascular symptoms and, when cases prove fatal, the cause of death is generally due to anaphylactic shock caused by sudden cardiovascular collapse, (hence the associated risk of heart disease).

Venom immunotherapy has been shown to be a highly effective treatment for venom allergy, often helping people who are especially vulnerable to insect stings, including those who work in jobs which expose them to stinging insects and people with systemic mastocytosis. It significantly improves most patients’ quality of life, although it does not help everyone.

Happily, although anaphylaxis rates for food and medications seem to have increased over the past few years, insect-related anaphylaxis rates appear to have remained relatively stable— or even to have decreased—and, even when an increase in hospital admissions for venom-induced anaphylaxis has been found, it has been significantly smaller than the increase in anaphylaxis cases to other triggers.

Importantly, there has been no increase in the number of deaths linked to venom-induced anaphylaxis, and Canadian and Australian numbers have even decreased. The reason for the decreasing numbers are unknown, but it may be related to the falling population (aka ‘colony collapse’) of bees and wasps that has occurred over recent years

Unknown triggers are dangerous because they hold the element of surprise

Cases of anaphylaxis in which the trigger remains unidentified—so-called idiopathic anaphylaxis—are more common than you may think; although the exact incidence of idiopathic anaphylaxis is unknown, the percentage of idiopathic anaphylaxis worldwide has been put at somewhere between 6.5 and 35% of all cases, depending on the criteria used.

Some researchers examining anaphylaxis data have found that the cause of a reaction can remain undetermined in most cases, even fatal ones.

Analyses of anaphylaxis deaths due to unknown causes can be complicated by the fact that many cases of anaphylaxis are coded as ‘unspecified’ in healthcare systems while the cause of death could actually be determined, which results in very inflated numbers (e.g. 19.3% in an American analysis and 63% in an Australian one). One analysis of anaphylaxis fatalities in Australia in which the researchers made a concerted effort to determine the cause of death of ‘unspecified’ reactions put the number of anaphylaxis deaths due to unknown causes over a 9-year period at 15 of 112 deaths (13%).

Although idiopathic anaphylaxis is a condition that can affect children, it’s much more likely to strike adults. A 2014 review estimated that idiopathic anaphylaxis accounts for around 10% of all cases of anaphylaxis in children and between 30 to 60% of cases in adults who are able to walk away from the event.

According to most reports, idiopathic anaphylaxis seems to be more common in women than in men, with over 2 in 3 cases affecting female patients, and it also seems to be more common in people who are known to have some type of allergy (i.e. are atopic). One American study also noted that African Americans were more likely to die from idiopathic anaphylaxis than their Caucasian and Hispanic counterparts.

The symptoms of idiopathic anaphylaxis are the same as anaphylaxis to any known trigger. They can can also be life-threatening and sometimes fatal. As with anaphylaxis to known triggers, children tend to have somewhat milder symptoms, often experiencing skin symptoms like hives, swelling or generalised flushing, although quite a few experience breathing difficulties. Sometimes people suffer from milder symptoms—like hives and/or swelling—to an unknown trigger in the run up developing idiopathic anaphylaxis.

The diagnosis of idiopathic anaphylaxis is one necessarily of exclusion—doctors try to determine the cause of the anaphylactic event but eventually have to admit defeat. Sometimes triggers are difficult to detect, sometimes they are simply not suspected. Triggers can remain unknown because:

• Food allergens are not tested for
• Food allergens are hidden (e.g. oral mite anaphylaxis, aka ‘pancake syndrome’)
• Triggers are unusual, such as latex, which should be suspected in a healthcare setting
• Exercise in combination with a(nother) cofactor make the determination of a case of food-induced anaphylaxis impossible to determine
• Alpha-gal syndrome (allergy to red meat), unlike other cases of IgE-mediated allergy, occurs hours after the food is eaten and is not suspected
• Undetected diseases such as a mast cell activating disorder like mastocytosis or female hormones can silently make a reaction more likely to happen

Idiopathic anaphylaxis can be successfully treated in the same way as anaphylaxis to a known trigger, with adrenaline first, and possibly antihistamines and/or corticosteroids after that to alleviate lingering symptoms.

People who suffer from repeated and relatively frequent episodes (i.e. more than 6 a year, or more than 2 in the space of two months) may be offered preventative treatment with medications like corticosteroids— e.g. prednisone, which has shown itself to be effective in reducing the number and severity of episodes–or mast cell stabilisers such as ketotifen. Some research has found that treatment with antihistamines is just as effective as corticosteroids in prompting improvements or remission.

A minority of people will need to take corticosteroids daily or every other day to keep episodes of idiopathic anaphylaxis at bay—these are known as cases of ‘malignant idiopathic anaphylaxis’—but long term treatment seems safe and effective.

The good news is that the majority of people with idiopathic anaphylaxis gradually get better over time, including people who have frequent episodes and have had to take medication regularly for years.

Image by Elisa Triviño on Pexels

Who is most at risk of a severe reaction?

Your risk of experiencing (severe) anaphylactic reactions depends on your personal characteristics and what you’re allergic to. Different age groups and different sexes tend to be vulnerable to different triggers, some of which are more dangerous than others and each of which is more likely to bother you at different times; for example, many people suffer from reactions to food in December, during the festive feasting season, fatal sting reactions are more likely to happen to outdoor lovers during the summer, and reactions to drugs tend to happen when people find themselves in need of significant medical care.

Any other diseases you have can also affect the timing severity of your reactions; for example, pollen allergies could put you at risk from experiencing anaphylaxis to plant foods during the relevant pollen season, and heart disease could affect both the severity of your reaction and your treatment for it.

When all is said and done, allergy risk is highly individual.

Children are more likely to experience anaphylaxis to food, but less likely than older children and adults to experience severe anaphylaxis

Children are much less likely to suffer from anaphylaxis than other age groups. A 2023 study of the global trends of all-cause anaphylaxis calculated an incidence rate of anaphylaxis among children in the general population of 5 cases per 100,000 children per year, compared to 20 cases per 100,000 adults per year. A study of children admitted to paediatric intensive care units (PICUs) in North America noted that ‘anaphylaxis occurred in 0.33% of patients younger than 18 years.’ However, the risk of anaphylaxis differs per trigger.

Food is the most problematic trigger for children—especially non-white boys. Children are about three times more likely to experience food-induced anaphylaxis than adults. Young children, especially, are more likely to experience anaphylaxis to food than to other triggers like venom or drugs, which become more important as a child gets older. From the age of around 2, more and more children experience serious reactions to venom and drugs until around the age of 10, after which the incidence of anaphylaxis to venom tends to stabilise while that of anaphylaxis to drugs stabilises during adolescence.

The foods most likely to cause anaphylaxis in young children—notably peanuts, nuts and milk—are also the ones that normally provoke the most severe reactions, except for egg which, although commonly involved in anaphylactic reactions, rarely ever causes the most severe symptoms. About 1 in 3 children with food allergies may be sensitised to multiple foods.

Reports of anaphylaxis to food tend to peak in very young children and in teens, with the most anaphylactic reactions in the 0 to 4 age group—in which an incidence rate of up to 7 per 100 food-allergic children per year has been reported—and in children older than 15 and young adults, by which point females are more likely to be affected than males.

Although infants and young children have a higher chance of experiencing food-related anaphylaxis and subsequent hospitalisation than other age groups, the reactions they experience tend to be less severe—with skin and respiratory symptoms being the most common. Fatal food anaphylaxis in this age group is very rare indeed. An analysis of European anaphylaxis registry data reported that just 0.9% (18 of 1970) of the cases involved infants, and only 1.3% (26 of 1970) of the children who had had anaphylaxis experienced life-threatening or fatal reactions.

In fact, infants are only considered at risk because the signs of infant anaphylaxis can be hard to recognise; some of them, like flushing, spitting and incontinence, for example, are normal daily occurrences in babies. More importantly, infants cannot verbally express their symptoms. The risk, therefore, lies not in how likely infants are to have a severe reaction, but in how likely caregivers are to recognise the symptoms and respond to them.

Cardiovascular symptoms like dizziness and fainting are more likely to affect teenagers, who are also more likely to need multiple doses of adrenaline than younger children.

Food is the least common cause of fatal anaphylaxis and, despite the majority of food-induced anaphylaxis admissions occurring in children less than 5 years old, fatalities that age group are incredibly rare and more likely to occur in older children.

Studies of food-induced anaphylaxis carried out in the UK, the US and Australia have found that fatalities are most common during the second and third decades of life, that is, in teenagers and young adults.

Teenagers and young adults are thought to have a greater chance of experiencing severe reactions to food than other age groups primarily because of the unnecessary risks they take, such as not reading food labels, eating foods that ‘may contain’ their trigger allergen or not always carrying their adrenaline auto-injectors.

But it could be that this age group is particularly vulnerable to food-related reactions because they have a lower threshold to their triggers or some other, as yet unidentified, ‘specific vulnerability’—as suggested by the authors of a British study that found that deaths from food-induced anaphylaxis peaked around the age of 25.

Additionally, many fatal reactions happen in people whose previous reactions have been so mild that neither they, nor their doctors, were likely to realise the potential severity of their allergy, and they were unlikely to have been prescribed an adrenaline auto-injector.

As it is, teenagers don’t really seem to behave more foolishly than anyone else. A survey of Scottish food-allergic adolescents found that most of their reactions appeared to result from accidents, misinformation or inexperience. Many reported reactions took place despite careful attempts to avoid allergens and with parental approval of the food. Ultimately, most teenagers seem to manage their food allergies as well as adults. According to the researchers, ‘Our data do not support the notion that high rates of severe reactions experienced by adolescents result from casual inattention, reckless behaviour, or a lack of awareness of their mortality.’

Multiple studies carried out in regions all around the world including Europe, the US, Canada and Asia have reported an increase in the rate of anaphylaxis experienced by children over the past 3 decades.

This reported increase in both emergency department visits and hospitalisations seems to be affecting children more than adults. Although an increase in anaphylaxis to both food and non-food triggers in children has been noticed, the main driver behind these relatively larger numbers is food, which has been responsible for some of the largest increases in anaphylaxis cases seen in recent years, especially in the under 15s.

Importantly, research from the UK and the US has also reported that, despite the increase in hospitalisations for food anaphylaxis in recent years, there has been no matching increase in fatalities (in fact, the UK has even registered a decrease).

Adults are more likely to experience life-threatening reactions, especially to venom and medications

Adults are much more likely to experience severe or fatal allergic reactions than children. Anaphylactic reactions tend to occur more often in middle age, and around 9 in 10 deaths from anaphylaxis tend to occur in adults.

Hospitals admissions and fatalities due to anaphylaxis caused by non-food triggers—notably insect venom and drugs—are much bigger problems during adulthood, with venom causing the most problems for the middle-aged and drugs for people older than 65.

Food tends to be the third most common trigger for anaphylaxis in adults, the most common trigger in the under-35s and the least common in people older than 65. The spectrum of frequent food triggers is broader in adults than it is in children, and adults are also more likely to be allergic to several food triggers.

When adults react to foods that are known to be dangerous, their reaction tends to be worse than that of their younger counterparts; a British study investigating anaphylaxis to peanuts and tree nuts, for example, found that adults were twice as likely to experience bronchospasm, almost four times as likely to experience severe throat swelling and about 9 times more likely to lose consciousness. Food, however, remains the least likely identified cause of fatal anaphylaxis among the usual triggers.

The tendency for food-allergic adults to often have worse reactions to food than children may be because they are more likely to be affected by cofactors, by a factor of at least 2 to 1. The most important cofactors are thought to be exercise, medications and alcohol.

Medications such as nonsteroidal anti-inflammatory drugs (NSAIDs), beta-blockers and angiotensin converting enzyme (ACE) inhibitors have all been reported as possible cofactors in cases of severe food-induced anaphylaxis. NSAIDs (notably aspirin) are particularly troublesome among people with food allergies. They are thought to make the gut more permeable and capable of absorbing food allergens and have been both linked to food-induced anaphylaxis and shown to exacerbate reactions in people with food-dependent exercise-induced anaphylaxis (FDEIA). They also seem to be particularly problematic for people who are sensitised to LTPs (lipid transfer proteins) in plant food.

Exercise—whose exact mechanism for worsening food reactions is unknown, but there are several options—often causes problems for adults with wheat allergy—hence the term wheat-dependent exercise induced anaphylaxis (WDEIA)—and it’s a particular problem for adults living in central Europe.

Alcohol can both cause allergic reactions itself and enhance food-induced reactions (possibly by increasing intestinal permeability and/or by increasing levels of IgE antibodies in the blood). It can also make things generally worse by contributing to adults’ risk-taking behaviour and masking the early warning signs of anaphylaxis. It would presumably do the same thing to children, but there aren’t enough drunk and anaphylactic children being taken to emergency rooms to be able to establish this as a fact.

The severity of anaphylaxis tends to increase with age. The older a person gets, the more likely they are to experience cardiovascular symptoms; by the time a person is over 65 years old, they are more like to experience cardiovascular symptoms (including loss of consciousness) than skin and/or respiratory symptoms, and this is the case no matter what the trigger, although venom- and drug-induced reactions are more likely to produce cardiovascular symptoms than reactions to food.

Severe symptoms are more likely among adults with drug allergies, people whose allergic reactions include exercise as a cofactor and those who have other serious diseases, such as chronic obstructive pulmonary disease, thyroid disease, diabetes and/or hypertension.

People with allergies and cardiovascular disease have double trouble because, not only does their condition puts them at risk of experiencing more severe anaphylaxis, the medications they may be taking for their condition could also make things worse or interfere with anaphylaxis treatment. This poses a dilemma for doctors who have to weigh the costs of using adrenaline and potentially putting the heart under further stress against the benefits of treating the allergic reaction; in the end, there is no substitute for adrenaline as a treatment for anaphylaxis.

Pro tip: Adrenaline given using an auto-injector is much safer than adrenaline that is administered intravenously (because of the risk of overdose). Doctors, however, are more likely to give people older than 50 an adrenaline IV because they erroneously assume that it will be safer. It is not. If you have an auto-injector and you are over 50, use it to avoid overenthusiastic adrenaline administration should you end up in hospital.

People who are middle-aged or older are much more likely to die from anaphylaxis than younger people. This is certainly the case when the reaction is caused by drugs or venom, but even in the case of food, where young children make up the majority of hospital admissions, fatalities are more likely to happen in older children and young adults, or people over the age of 80.

The elderly may be at particular risk of dying from anaphylaxis because they do not have the physiological capacity to deal with the complications of anaphylaxis—i.e. low blood pressure (hypotension), low levels of oxygen in the body (hypoxia) and/or abnormal heart rhythms (arrhythmias)—or the side effects of using adrenaline.

However, the increased risk in this age group may also be related to the fact that people with comorbidities like cardiovascular disease, which older people are more likely to have, run the highest risk of a fatal allergic reaction, and/or the fact that the drugs used to treat these kinds of diseases often exacerbate or even cause allergic reactions themselves.

Ultimately, it’s difficult to say whether it’s advanced age, comorbidities or the use of medications to treat those underlying physical conditions that actually make reactions worse but, if you’ve made it to what is generally considered ‘older age’, your chances of having severe anaphylaxis requiring professional medical help to a trigger are relatvely high regardless of whether you have a weak heart and/or are taking medication for something,

Your risk of anaphylaxis depends on your sex

Boys are more likely to experience anaphylaxis than girls, but women are more likely to experience it than men. Studies carried out worldwide—in a variety of settings from doctor’s offices and hospital critical care units to private allergy clinics and people in the community—have revealed that, during childhood, boys are more likely to have allergic diseases and to experience anaphylactic reactions than girls, but that this pattern reverses itself in adulthood, with women being more likely to experience anaphylaxis than men. The switch tends to happen during puberty, between the ages of 10 and 15 years old, with cases of anaphylaxis in women peaking when they reach middle age.

This distinction has been found in cases of anaphylaxis provoked by both food and non-food triggers like drugs. (And anaphylaxis to seminal fluid (sperm) is only reported in women, although it’s possible that some men may be allergic to their own semen too).

Why women are more prone more to allergic reactions than men during adulthood is unknown, but the influence of sex hormones is strongly suspected, although the exact mechanisms still need to be clarified.

However, men are more likely to experience anaphylaxis to certain foods than women and possibly more likely to experience life-threatening and fatal reactions. Even though women are more likely to experience anaphylaxis to food in general, men seem to have a higher risk of experiencing anaphylaxis to meat and wheat. Men (but not boys) have also been found to have a slightly higher risk than women of experiencing more severe anaphylactic reactions in general (at least until they reach their late fifties), although some research from Australia and the US finds that women are at greater risk of experiencing fatal reactions and reactions that require hospitalisation, so this point is still up for debate.

Men are more likely than women to experience fatal anaphylaxis from any cause, but especially venom, and especially if they are relatively old and white. Why this is so is unknown, but experts suspect that white men may be more likely to have outdoor or high-risk (for the purpose of this topic) occupations like beekeeping, and that older men in general are more likely than women to have other underlying health issues (like heart disease) that put them at greater risk of dying during a severe reaction.

Non-whites may be at greater risk of experiencing anaphylaxis

Several studies suggest that non-whites may be at risk of suffering more from their allergies. For example, a British study that explored the association between anaphylaxis and ethnicity found that children from families of South Asian descent (i.e. Indian, Pakistani and Bangladeshi) living in Birmingham were around 1.5 times more likely to experience anaphylaxis than their white counterparts, and 5 times more likely to have severe anaphylaxis, an observation that was apparently not due to socioeconomic factors. An analysis of UK Fatal Anaphylaxis Registry data also revealed an excess of deaths in boys of African, Middle-East or Far-East descent due to cow’s milk allergy.

In the US, several studies have produced similar results. A 2015 study of paediatric emergency department visits and hospitalisations in Illinois found that Asian and Hispanic children were more likely than children of other ethnicities to visit a hospital’s emergency department because of food-induced anaphylaxis, and another study investigating fatal anaphylaxis in the US found that African Americans (who have also been shown to have a higher risk of having allergies and severe asthma) were more likely to die as a result of anaphylaxis to food, drugs and ‘unknown’ triggers than people of other ethnicities.

In New Zealand, a study of children treated in hospitals for food–induced anaphylaxis found that the largest number of cases involved Asian children, followed by Pacific children, Maori children and, finally, New Zealanders of European descent. Among adults, Pacific Islanders have been shown to make up the largest number of anaphylaxis cases seen in hospitals.

Unlike British research, American research finds that these differences may well be—at least partly—due to socioeconomic factors, including access to healthcare and environmental exposures (e.g. to cockroaches and dust mites, which are associated with sensitisation to food and respiratory allergens). Furthermore, the higher prevalence of fatal drug-induced anaphylaxis in African American people might reflect worse physical health, greater medication use and less access to healthcare.

The explanation is probably not entirely straightforward, however; for example, an analysis of anaphylaxis data involving children admitted to hospital in North America found that, compared to other races, there were more Asian/Indian/Pacific Islanders younger than 2 years admitted for anaphylaxis, but fewer Asian/Indian/Pacific Islander adolescents. Furthermore, significantly more children of mixed race between the ages of 2 and 5 years were admitted for anaphylaxis than all other races, implying that other factors are also at work.

Similarly, an Australian study that found that infants whose parents were born in East Asia were more likely to have peanut allergy than those whose parents were born in the UK/Europe reported that this only occurred for a single generation and was not present among infants with parents migrating from other countries, suggesting that the greater problems experienced by non-white children with allergies are probably due to interactions between their genes and their environment.

People with concomitant diseases are more likely to suffer severe reactions

People who experience anaphylaxis tend to have other allergies and medical conditions, which are often age-dependent; for example, eczema and respiratory allergies tend to affect preschoolers and older children, respectively, whereas pollen allergies, lung disease and thyroid disease are more likely to affect adults.

Three of the most common concomitant diseases (aka comorbidities) are asthma (which often affects children with food allergies), mastocytosis (which often affects middle-aged adults with venom allergy) and cardiovascular disease (which often affects older adults).

Asthma is often mentioned as a risk factor for severe reactions, normally to foods (especially to certain foods like peanuts, tree nuts and wheat). Asthma has long been associated with food allergy, although the exact relationship between the two is still not fully understood; whatever the underlying reason, young children with food allergy are more likely to develop asthma than children without food allergy, and studies have found that people who have both food allergies and asthma are at greater risk of experiencing severe asthmatic episodes.

Likewise, research has also found that that severe wheeze is a prominent feature of serious reactions to food, that people with foods allergies and a history of asthma are more likely to suffer from severe anaphylaxis and around 5 times more likely to suffer from anaphylactic shock than people without asthma, and that children who need multiple doses of adrenaline are more likely to have asthma than children who need a single dose.

Multiple studies from around the world that have examined fatalities due to food-induced anaphylactic reactions have also noted that the majority of the people involved had asthma and that death is generally caused by difficulty breathing leading to respiratory arrest.

So it makes sense to think that asthma and/or underlying airway hyperresponsiveness (bronchial hyperactivity) are considered likely to be significant risk factors.

That said, asthma is not, in itself, a predictive factor for severe or fatal anaphylaxis; food anaphylaxis (including fatal anaphylaxis) frequently occurs in people without coexistent asthma, and around half of food-allergic children have asthma, yet few of them will ever experience severe anaphylaxis and almost none will experience a fatal food-allergic reaction.

What may be important is how controlled the condition is; some studies have stated that fatal reactions to food occurred in people who had active or poorly-controlled asthma and have found that pathological evidence suggests that asthma exacerbation might be linked to fatal food reactions.

In a report examining the cause of anaphylaxis-induced deaths recorded in the UK register, British allergist Dr Richard Pumphrey comments that most fatal reactions to food are the result of relatively mild reactions turning fatal because the reaction exacerbates a person’s existing asthma. As such, ‘Optimal daily control of asthma is crucial in reducing the risk of a fatal reaction in those with food allergy.’

However, it’s unclear whether poor asthma control is a risk factor for more severe anaphylaxis because that type of data is often not collected and, when it is, it can be contradictory depending on the definition of severity that is used. Some research has also reported anaphylaxis fatalities in people whose asthma was well-controlled. Ultimately, the best advice that can be given on this subject is to take extra care with your food if you feel unwell.

Mastocytosis is also mentioned as a risk factor for more severe allergic reactions. Mastocytosis is a rare disorder (affecting maybe 1 in 10,000 to 20,000 people) in which mast cells—the cells responsible for releasing the bulk of the histamine during allergic reactions—are increased in number, either in the skin—cutaneous mastocytosis, which typically affects infants and toddlers—or the bone marrow, bones, digestive system and lungs—systemic mastocytosis, which mainly affects adults. It’s the latter version that people with allergies have to worry about. However, a person with mastocytosis is no more likely than one without the condition to have allergies.

Mastocytosis is not involved in all allergic reactions equally; it is, by its very nature, likely to be involved in and confused with cases of idiopathic anaphylaxis, but the known trigger it is most often associated with is insect venom, which is why people with mastocytosis who have a systemic reaction to insect venom are advised to be maintained on venom immunotherapy indefinitely.

High levels of tryptase (a protease enzyme released primarily by mast cells) are suggestive of mast cell disorders like mastocytosis and tests measuring tryptase levels normally present in people’s blood are sometimes to identify people with allergies who might have a bigger risk of experiencing severe reactions. These tests have shown an association between high tryptase levels and a risk of suffering severe anaphylactic reactions to insect venom, but their use in identifying people with food allergies who may have a bigger risk of experiencing severe anaphylaxis and, as result, a possible mast cell disorder like mastocytosis is disputed, with some studies finding a correlation between tryptase levels and severe reactions to food—or certain foods, like nuts but not milk—and others, finding no such correlation.

All in all, about 50% of adults with mastocytosis will experience anaphylaxis, whereas only about 10% of children with mastocytosis will, and those that do are more likely to have extensive skin disease. When someone with mastocytosis does have anaphylaxis, it’s more likely to be a severe grade 5 reaction, often resulting in unconsciousness.

Skin symptoms are rarely ever associated with mastocytosis, so when a person passes out during a severe reaction after being stung by an insect or to an unknown trigger, the absence of skin symptoms like hives (urticaria) or swelling (angio-oedema) is a sign that that person may have mastocytosis.

Another condition that is often mentioned in association with severe anaphylaxis is cardiovascular disease. People with cardiovascular disease are also prominently represented among anaphylaxis fatalities.

The heart is both a source and the target of chemical mediators released during anaphylaxis; it contains an abundance of mast cells and the mediators released by those mast cells often target the heart muscle and its arteries. To make matters worse, a person with cardiovascular disease already has damaged heart muscles and arteries, and a damaged heart muscle contains even more mast cells that produce even more inflammatory mediators, and damaged arteries are more susceptible to them. To make things even worse, during anaphylaxis, the decreased blood flow to the coronary arteries can lead to further damage to the heart muscle. Anaphylaxis can even provoke a heart attack, known as Kounis syndrome.

In a final, ironic twist, people with cardiovascular disease—often older people who are more likely to suffer cardiovascular symptoms during anaphylaxis—are more likely to be using medication that treat things like high blood pressure and angina, and those medications themselves may make reactions worse by decreasing the threshold of mast cell activation and/or by reducing the effectiveness of adrenaline treatment. However, whether this is actually the case is severely disputed, not least because it’s difficult to disentangle the effects of medication, age and heart disease from one another.

People with food allergies who live in areas with less sunlight may be more likely to experience anaphylaxis

Several studies have linked sunlight with the development of food allergy, possibly because underexposure leads to a lack of vitamin D, which may protect against allergy, although the actual cause of the association still needs to be determined.

Similarly, studies carried out in countries which have wide variations in latitude and therefore populations that are exposed to different amounts of sunlight—namely the US, Chile and Australia—have reported more prescriptions of adrenaline auto-injectors as well higher hospital admission rates because of anaphylaxis in regions with less sunlight.

The effects of sunlight are more commonly observed in people with food allergies, especially children whatever their sex or race.

An American study also revealed that the increase in new cases of anaphylaxis in the US seems to be limited to areas of limited sunlight, finding an increase in the incidence of anaphylaxis in children (of 7%) and adults (of 2%) living in New York state, but no increase in anaphylaxis rates in sunnier Florida.

Image by Volodymyr Hryshchenko on Unsplash

Image by Marc Pell on Unsplash