Adult-Onset Food Allergy; Definitely a Thing

Image by the Irritated geek

While food allergies have traditionally been viewed as a concern for children, new food allergies can develop at any age. The phenomenon of adult-onset food allergy has gained increasing recognition in recent years, in large part because it’s become clear that, not only are there more allergic adults around that previously suspected, it’s a growing problem—in fact, the number of adult with food allergies is now considered to be at a historic high.

The population of food-allergic adults is made up of two, often overlapping, categories: people with childhood allergies that have persisted into adulthood—notably to peanuts, tree nuts and seafood—and people who develop new allergies in adulthood. The number of people in both of these categories is increasing.

The fact that adult food allergies are still unexpected and come with symptoms that are often slightly different to those seen in children means that it generally takes longer for an adult to get a proper diagnosis. Unfortunately, once acquired, an adult-onset food allergy tends to be a persistent problem for most people. There are, however, ways to manage it successfully.

This page will answer the following questions:

How common is food allergy in adults?

The world of allergology is only just waking up to the idea of food allergy in adults, so research on the topic is still rather sparse. Global prevalence numbers of food allergy in adults range (very roughly) between about 1 in 100 people (southern India) to 1 in 10 individuals (the US) to 1 in 6 (Mexico).

A decades-old review mentions an estimated worldwide prevalence of adult allergy of 3.2%. A German study of Berliners carried out around the same time put the rate of confirmed food allergy among the adult population at 3.7%.

More recently, a 2023 review based on 110 studies carried out in European countries (as defined by the United Nations) as well as Greenland and Turkey put the prevalence of self-reported food allergy among adults at 22.8% when it came to ever having had a food allergy, and at 12.3% when adults were asked whether they were suffering from one at the time of the survey. The equivalent prevalence numbers of doctor-diagnosed allergy were 5% and 6.9%, respectively.

A 2019 study looking into the prevalence of adult allergy in 6 European centres put the prevalence of probable allergy (self-reported symptoms plus matching blood test results to 24 tested foods) in adults at 0.3% in Athens (Greece), 1.4% in Reykjavik (Iceland), 2.1% in Utrecht (the Netherlands), 2.8% in Łódź (Poland), 3.3% in Madrid (Spain) and 5.6% in Zurich (Switzerland).

In the US, an analysis of 2015-2016 survey data involving 40,443 adults found convincing IgE-mediated food allergies (symptoms fitting a list of criteria put together by a panel of experts) in 10.8% of them. Almost half (48%) of them reported developing at least one new food allergy during adulthood and just over a quarter (26.9%) developed their first food allergy during adulthood.

An analysis of medical records collected from a network of Chicago-based Northwestern University allergy clinics around a year earlier reported that at least 15% of the patients seen by doctors had developed their food allergies during adulthood, generally around the age of 31.

In Mexico, where 1126 adults were surveyed between December 2012 and April 2013, 188 (16.7%) were found to be suffering from a food allergy (as defined by criteria for signs and symptoms determined by a panel of European experts).

In the Middle East, a 2020 study of 5497 Saudi Arabian students (average age 22) enrolled at a large university between 2008 and 2018 reported a prevalence of physician-diagnosed food allergy of 9.6%. About 1 in 5 (19.2%) of those students reported an adult-onset food allergy. A nationwide survey of adults in 2020 revealed a self-reported prevalence of food allergy of 21.4%, peaking among the 20- to 29-year-olds before slowly decreasing again.

A survey of Kuwaiti students at Kuwait University carried out between 2015 and 2016 reported that 5.4% of them met the criteria for physician-confirmed IgE-mediated food allergy.

In south India, the prevalence of probable food allergy (self-reports of symptoms plus specific IgE to the same food) in adults has been reported to be 1.2%.

And a 2012 study based on a mixture of lab tests and convincing symptoms has put the prevalence of adult food allergy in Taiwan at 6.4%.

Sadly, once you acquire a food allergy as an adult, you’re likely to keep it although, according to American data from the Food Allergy Research & Education (FARE) Food Allergy History Survey, around 1 in 5 adults regain tolerance to their former food nemesis.

Image by Fernando Paleta on Pexels. .

Why do new food allergies appear in adulthood?

Although allergists are not sure why adults who’ve gone through childhood without allergies suddenly become allergic to food, there are several working theories on the subject.

Loss of tolerance

One of the possible mechanisms put forward for the development of adult-onset allergy is loss of tolerance. This is the idea that, after a long period of not eating a certain food, we may lose our ability to eat it without provoking an immune reaction. This idea is backed up by research which has found that children with eczema (aka atopic dermatitis) and other allergic diseases who are put on lengthy elimination diets can develop worse reactions to their food trigger when it is reintroduced into their diet.

Similarly, children who outgrow their peanut allergy but don’t start eating peanuts regularly run the risk of their allergy returning, unlike their peers who incorporate peanuts into their diet.

Although most of this type of research involves children, atopic adults who eliminate a food trigger from their diet (often on the recommendation of a health care provider) have also been shown to be at risk of developing severe IgE-mediated symptoms to that food, like the case of a woman who ate peanuts regularly for many years without problem before being told to avoid them by a doctor after a positive skin test response—which, incidentally, was surprisingly bad advice, because the results of skin tests only show potential sensitisation and not allergy and should never be used as a reason to avoid a food that has previously not provoked any symptoms. When she did eat peanuts again, she developed respiratory symptoms.

Barrier damage

Another reason that adults are at risk of developing new allergies is our continued exposure to things that break down our physical defences against (food) allergens.

In 2007, professor Gideon Lack proposed the dual-allergen-exposure hypothesis, which proposes that allergic sensitisation to food doesn’t just occur through the gut but can also occur through damaged skin.

Since then, research has shown a clear link between eczema and food allergy in children finding, for example, that young children with eczematous skin are more likely to become sensitised to peanuts if their family eats peanuts at home. Studies have also shown that food allergens can be found everywhere; in the air in people’s workplaces, at food markets and in people’s homes.

Now we also have evidence supporting the more recent epithelial barrier hypothesis, which states that the chemical substances and environmental pollutants that we are exposed to throughout our lifetimes—aka our our external exposome—damage the barriers of our skin, gut, and respiratory tract, and this makes us more vulnerable to various types of allergies.

Over 200,000 new chemicals have become common (especially) in developing countries since the 1960s thanks to modernisation, urbanisation and globalisation, and multiple studies show that they have not been beneficial to our natural barriers.

Ultraviolet radiation and air pollutants like cigarette smoke, diesel exhaust, ozone, microplastics, and nanoparticles induce oxidative stress in our skin—inflammation, loss of elasticity, hyperpigmentation, uneven texture and tone, disruption to our skin microbiome—and activate our immune systems.

Exposure to toxic substances in our homes and workspaces, such as dishwasher and laundry detergents, household cleaners and commercial detergents and volatile organic compounds (VOCs) commonly found in wallpaper, furniture and plastics damage our skin barriers further, as do common indoor and outdoor allergens like house dust mites and pollens which contain proteolytic enzymes that are capable of breaking down the proteins in our skin, making it more permeable, as well as activating our adaptive immune response.

And that’s just the stuff we come into contact with by accident. We also ingest problematic substances including medications (more on those later) and processed foods.

Processed foods contain a bunch of problematic ingredients, but some of the worse are emulsifiers, which are used to prevent separation and extend shelf life. These emulsifiers act in a similar way to detergents and are suspected of being involved in the development of Crohn’s, (1) Type 1 diabetes, coeliac disease and IBS, as well as definitely altering the composition of our gut microbiota. This, in turn, is associated with increased gut barrier permeability and an increased risk of sensitisation to food allergens, with certain bacteria being more likely to provide a protective effect against the development of food allergy than others.

Ultra-processed foods also tend to be low in fibre, which will give you less protection against developing a food allergy. A diet that’s high in gluten or glucose has also been shown to increase intestinal permeability and to damage the epithelial barrier of your airways, too.

All of this damage to the epithelial cells of the gut, skin and airways allows food allergens in, causing sensitisation that produce food allergen-specific IgE antibodies and can eventually lead to immediate (‘classic’) type food allergies.

Which helps to explain why studies of adults with food allergies often find that those adults are more likely to suffer from diseases like hay fever, eczema and asthma than healthy adults, although people with childhood-onset allergies are more likely to suffer from asthma and eczema and people with adult-onset allergies are more likely to suffer from hay fever (hence the high prevalence of pollen food allergies in that demographic).

Sex hormones

Numerous studies and reviews have found that, when it comes to typical, IgE-mediated allergy, although childhood allergies are more likely to affect boys, in adulthood, there is a reversal in fortunes and it’s women who are at greater risk of developing allergies and intolerances to food.

This reversal in fortune happens after puberty, peaks in middle age and diminishes again in menopause. By adulthood, the ratio of women to men with food allergy is around 6:4.

There are also sex differences in the types of food most likely to cause reactions, with women being more likely to react to fruits and berries and men to peanuts—although, when they do have peanut allergy, women are more likely to have severe reactions. And although some studies may report that men are more likely than women to be allergic to peanuts, studies carried out in the UK and Norway contradict this, so the idea that women may at least have a natural advantage with this one food may be wrong, too.

Among adolescents and young adults, women report more food-induced complaints (and more reactions to aeroallergens and nickel) than men, are more likely to be affected by gastrointestinal and skin reactions, and generally report a worse health-related quality of life. Women are also more likely to suffer from severe reactions, including anaphylaxis.

Not only are women more likely than men to have the ‘classic’ IgE-mediated allergy to food (and food additives), as well as Pollen Food Syndrome, they are also more likely to develop the non-IgE-mediated conditions (or mixed, meaning both IgE-mediated and non-IgE-mediated) of eczema and food protein-induced enterocolitis (FPIES). Men, on the other hand, are more likely to develop eosinophilic oesophagitis.

Hormonal fluctuations also play a role in both the development of food allergy and the manifestation of symptoms, with some women developing a new food allergy during or soon after pregnancy, and others reporting a worsening of their symptoms during menstruation. (2)

Although other factors could be involved in these sex differences, such as women’s greater tendency to report symptoms than men, or the fact that they are more likely to use medications (which can also worsen allergic reactions), the fact that skin prick tests seem to produce larger responses (in both food-allergic and healthy women) on days 12–16 of their menstrual cycle (during peak oestrogen levels), points to the clear influence of hormones on immune system reactions.

While oestrogen’s role in allergy has not been fully worked out, it seems to make the immune system more likely to produce allergic reactions. It increases the production of immunoglobulin antibodies and also seems to promote the development of delayed, non-IgE-mediated allergic diseases. It also increases mast cell reactivity, thereby reducing the amount of allergen that’s needed to provoke symptoms.

Testosterone, on the other hand, tends to suppress the immune response by, among other things, reducing immunoglobulin production. Men also seem to have higher concentration of IgG4 antibodies in their blood, which are though to prevent the stimulation of mast cells, possibly by blocking the allergen from binding to IgE-antibodies present on the cells.

Although the mechanisms by which sex hormones work to promote allergic responses in women and suppress them in men still need to be clarified, the fact that oestrogen does seem to give women such a natural disadvantage in this area does give us at least one reason to look forward to the menopause.

Increased impact of cofactors

There are certain things called cofactors which are thought to make allergic reactions more likely to happen and/or more severe. They are thought to work, in the main, either by lowering a person’s threshold to an allergen, meaning that they need less of it to provoke a reaction, and/or by increasing the body’s allergen uptake by, for example, making the gut more permeable, meaning that more of the allergen is bioavailable, i.e. able to be absorbed and used by the body.

Although cofactors also affect children, they tend to play a more important role in adult allergy and are thought to be involved in around 30% of anaphylactic reactions in adults vs 14% to 18.3% in children. This is probably less because of biological factors and more because they are more likely to be part of an adult lifestyle. This is also the reason why the most common cofactors differ in adults and children, with adults being more likely to suffer the consequences of combining food triggers with:

• Exercise
• Nonsteroidal anti-inflammatory drugs (NSAIDs), including aspirin and Ibuprofen
• Alcohol
• Sleep deprivation and stress

Exercise is the most well-known cofactor because it is responsible for the majority of reactions in food-dependent exercise-induced anaphylaxis (FDEIA)—which, despite the name, does not always need exercise to provoke a reaction—and the vast majority of food-dependent exercise-induced anaphylaxis reactions occur in adolescents and adults.

Alcohol—which can promote sensitisation to food allergens in the elderly when consumed in large amounts on a regular basis—can both increase the severity of allergic reactions to food and the likelihood of a reaction occurring in the first place due to inattentiveness and a general tendency to throw caution to the wind.

Exercise and alcohol are especially likely to play a role in allergic reactions that adults have to wheat (aka wheat-dependent exercise-induced anaphylaxis, WDEIA).

When it comes to medications, NSAIDs are the most common type of drug involved in cofactor-induced allergic reactions, but all sorts of medications have been reported as cofactors in reactions to food, including beta-blockers, angiotensin-converting-enzyme (ACE) inhibitors and antacids, the latter of which are particularly popular among older age groups.

Medications tend to be more of a problem for people the older they get, partly because of the fact that older people generally have to take more of them, providing more opportunities for allergic reactions, partly because the medications that they take can make reactions worse, and partly because the medications that adults have to take actually have multiple ways of interacting with allergy.

Antacids, for example, can cause several types of allergy problems. First, by suppressing the levels of gastric acid in the stomach, they inhibit proper digestion and make people who are already allergic to a food more likely to suffer a severe reaction because there are more intact food proteins present in their digestive system to interact with their immune systems.

Second, antacids may provoke new (food) allergies. There is evidence to suggest that encouraging more intact food proteins to linger in the digestive system may prompt older patients who need them for GI problems to become sensitised to those food allergens and may even put the offspring of pregnant women who need them for heartburn at a higher risk of developing allergies.

Antacids are even suspected of being responsible for the increase that has been observed in cases of eosinophilic oesophagitis.

Often, one or more cofactors together with one or more types of food allergen are needed to produce a reaction.

In 2018, the results of a study that followed 157 food-allergic adults over the course of a year revealed that about half (46%) had a reaction to food during that time. In around 3 in 4 (74%) of the cases, at least one cofactor was thought to be present. In just around half (47%), more than one cofactor was involved. Reported cofactors included tiredness (38%), alcohol intake (16%), hay fever (16%), stress (14%), asthma (9%), infection (3%), exercise (3%) and medication (2%). In this group of people, there was no link found between cofactors and reaction severity, the cofactors just influenced the likelihood of having a reaction.

Other cofactors include body temperature and the way food is prepared. You can read more about cofactors here.

The ageing process

As we age, several of the natural consequences of ageing make us more vulnerable to developing food allergies.

For a start, there’s the problem of immunosenescence, which is the gradual deterioration of the immune system that comes with advancing age. It involves a whole range of changes to the mechanisms of both the innate and adaptive immune systems which are too complex to understand in a hurry go into, but which ultimately result in, among other things, the skewing of adaptive immunity towards a (Th2) profile which favours allergic responses and a lingering level of low-grade inflammation known as ‘inflamm-aging’.

Inflamm-aging, in turn, increases intestinal permeability, letting more food proteins into the blood and increasing our risk of losing tolerance to foods that we previously ate without causing problems. And age-related deterioration doesn’t just affect the whole immune system, it also affects local immune responses on the gastrointestinal mucosa (the mucous membrane layer of the stomach and gut) where tolerance induction becomes gradually impaired as we get older, meaning that the intake of new foods can potentially induce sensitisation to new food allergens.

Additionally, older people are prone to chronic conditions like atrophic gastritis that lower gastric pH, and a less acidic environment in the stomach means that more food allergens are able to remain intact and better able to provoke a response when they are absorbed through the gut barrier. Prolonged courses of antacid treatments (like proton-pump inhibitors) also produce less acidic stomach environments and have been linked to an increased risk of food allergy.

And then there’s the ‘anorexia of aging’, which is the tendency we have to lose our appetites and eat less as we get older, meaning we take in fewer nutrients (nutrients that are bodies are less able to absorb in the first place). Unfortunately, a lack of micronutrients like vitamin D, zinc and iron may also increase the risk of developing allergies as they all work on our immune system in ways that help to promote tolerance.

A poor diet is also bad for our gut microbiome, which is already negatively affected by immunosenescence and by other factors associated with older age, such as having to take more medications such as antibiotics, which are often wrongly prescribed to older people and are known to negatively affect the composition of our gut microbiota. And a dysfunctional microbiome promotes inflammation that further degrades the gut barrier, letting in more allergens for us to react to.

Finally, the gut barrier is not the only barrier that suffers with age; a deterioration in skin quality is one of the more obvious signs of old age; it becomes thinner, more fragile and starts to lose its ability to repair itself. As such, it becomes less of an efficient barrier. All of these things may contribute towards a higher risk of developing (worse) eczema and, even though food is less likely to induce AD symptoms in older people than in children, older people with moderate-to-severe AD are more likely to be sensitised to food allergens than those with milder AD.

Also, much like the gut, older skin suffers from reduced bacterial diversity and a decrease in beneficial microorganisms (although the exact role that this may play in the development of AD still needs to be established). To cap it all off, older skin is more prone to itching, and scratching will damage its barrier function further.

Image by Freepik on Freepik .

What does food allergy look like in adults?

The ‘classic’ type food allergy that most people think of when they think of a food allergy is currently considered the most widespread and fastest-growing human health condition among adolescents and adults.

This type of allergy is developed when a person eats something and their body’s immune system decides that that food is a threat and produces IgE antibodies designed to identify said food and produce a defensive response the next time the person eats it.

Adults who have IgE-mediated food allergies fall into 3 categories; those who have not outgrown their childhood food allergy, those who have developed a new food allergy during adulthood and those who fall into both of those categories.

The main differences between childhood and adult food allergies are the most common triggers and the symptoms they provoke. The most common childhood food allergies in Western countries are milk, eggs, peanuts, tree nuts, shellfish, wheat and soy.

Although many children outgrow their allergies to milk, egg, wheat and soy, US researchers have found surprisingly high rates of adult-onset allergy to these typical ‘childhood’ allergens; national survey data suggests that Americans are actually more likely to develop an allergy to wheat in adulthood, with just over half (52.6%) of the wheat-allergic reporting an adult-onset allergy, and almost half (45.4%) of those allergic to soy also developing their allergy during adulthood.

And, unlike the symptoms experienced during childhood, reactions to these triggers tend to be severe. Wheat is the most common trigger of anaphylaxis—notably wheat-dependent exercise-induced anaphylaxis (WDEIA)—among adults in Central European countries as well as among Japanese and Thai adults on the other side of the world.

Likewise, although egg and milk allergy were previously thought to be easily outgrown during childhood, new data suggests that those allergies are increasingly likely to persist into young adulthood, for reasons as yet unknown. As such, American survey data reveals that milk is the second most common food allergy among the adult population, with just over 1 in 5 (22.7%) adults reporting that they acquired their allergy during adulthood.

Reports of convincing adult-onset milk allergy become increasingly common as Americans get older; among people aged between 18 and 19, for examples, only 12% report a new allergy to milk after the age of 17, whereas among those aged over 60, 30% report a new allergy to milk after the age of 17. Research from Western China also finds that people older than 70 have increased sensitisation to cow’s milk, and Dutch research reveals that cow’s milk’s is the most common allergen affecting adults with severe eczema.

A global review of anaphylaxis cases published in 2021 reported that, in Europe, cow’s ‘milk appeared to cause a higher proportion of anaphylaxis in adults compared to peanut given the reported prevalence of allergy to those triggers.’ It’s not just cow’s milk that adults have to watch out for; mare’s milk and goat’s milk can be problematic, too.

Egg is only the 6^th most common food trigger among adults in the US, with almost a third (29%) reporting an adult-onset allergy, but a nationwide survey of just over 4700 adults in Saudi Arabia revealed it to be the most common food allergen in that country, with an estimated prevalence of 3.7%.

Although adults do get the classic form of egg allergy, much of the research carried out on egg-allergic adults in the West has focused on the more commonly seen form of adult-onset egg allergy, bird-egg syndrome.

Bird-egg syndrome is a condition in which a person is sensitised to egg, normally the yolk, by breathing in bird allergens from feathers, excrement or bird serum. Although bird-egg syndrome can affect children, the vast majority of people who get it are adults, notably women.

The first report of bird-egg syndrome was of a 65-year-old Dutch woman who, after getting a pet parrot, developed hay fever symptoms which were later followed by rashes and swelling (oedema) whenever she ate eggs. Cases have also been reported of people contracting it through their pet lovebirds, budgies and canaries.

Bird-egg syndrome causes both respiratory symptoms (rhinoconjunctivitis—hay fever-type symptoms—and asthma) and food-allergy symptoms, which tend to appear a little later than the respiratory symptoms and differ from the classic egg allergy by mainly consisting of gastrointestinal symptoms (e.g. stomach cramps, vomiting and diarrhoea) rather than skin symptoms.

Because the allergen responsible for this cross-reactive allergy is vulnerable to heating, people with bird-egg syndrome can still eat hard-boiled egg yolks. Allergic reactions to chicken meat also occur, but they are rare and normally limited to oral allergy syndrome.

Although this type of egg allergy is often persistent, rare cases of acquired tolerance to raw or soft-boiled egg yolk have been reported in people who are no longer exposed to birds.

Allergies to peanut and tree nuts, seeds, fish and shellfish are also known to be persistent but they are also among the most common triggers of adult-onset food allergy.

Peanut allergy is the 3^rd most common trigger of food allergies in American adults, estimated to affect around 4.6 million, roughly 1 in 6 of whom had their first reaction during adulthood. According to Dutch research, it’s also the most common plant-food trigger in adults with severe eczema. Tree nuts are the 4^th most common trigger of food allergies in American adults, affecting around 1.2%.

As well as being particularly persistent, (pea)nut allergies are reported to produce the most severe reactions in British, Canadian and American adults.

Seafood allergy, notably an allergy to crustaceans, is the most common trigger of reactions in adults in many parts of the world, especially in Asian countries, where it is also the most common cause of severe reactions to food.

The high rate of shellfish allergy in that particular part of the world is due both to the fact that shellfish is a staple food in the region and to the fact that many people who live there are sensitised to house dust mites and cockroaches which thrive in the warm and humid conditions, and both insects are highly cross-reactive with shellfish.

As such, an association between sensitisation to house dust mites and/or cockroaches and shellfish allergy has been shown in adults living in Hong Kong, Thailand and mainland Malaysia.

However, insects, especially dust mites, can be found everywhere, and the same kind of link has been noted in adults in southern India and coastal cities in Iran, as well as adults in Algeria, Gabon, the Democratic Republic of Congo, the Canary Islands, Poland, Canada and the US.

In America, almost half (48.2%) of all cases of shellfish allergy develop during adulthood, and it has been described as a particularly enduring allergy, showing lower rates of decrease across the life span than other food allergies. Some experts suspect that this persistence may be due to a booster effect from the cross-reacting insect allergens that people are exposed to every day.

A link has also been noted between a sensitisation to house dust mites and food-adjacent allergy to the parasite anisakis simplex, which affects adults who are partial to undercooked fish and squid.

This parasitic nematode (roundworm) causes problems by infecting people—a condition known as anisakiasis. Anisakis essentially buries itself in a person’s innards (specifically, the walls of the oesophagus, stomach or intestine) and causes symptoms that look a lot like allergy—stomach pain, nausea, vomiting, diarrhoea. However, having done that at least once, it can also sensitise people who then become allergic to the worm itself and suffer from typical symptoms of allergy such as rashes, facial swelling (angio-oedema), asthma, stomach pain and occasionally anaphylaxis.

Anisakis can infect anyone who eats undercooked fish that has become an unwitting host to the worm, making it relatively common in countries in which marinated and/or raw fish is a culinary tradition; Japan (sushi), Nordic countries and Holland (gravlax, salted or pickled raw herring), Spain and Italy (marinated fresh anchovies, aka boquerones and alici marinate, respectively), Hawaii (lomi lomi salmon) and South America (ceviche).

Special mention: alcoholic drinks & cannabis

Allergies to alcoholic drinks and drugs are only reported in adults, simply by virtue of the fact that drinking and taking recreative drugs are overwhelmingly adult pastimes.

Allergic reactions to beer have been reported (because of the wheat and the barley) and to wine (because of the grapes and the sulphites) and to drinks like craft beers and cocktails because of various plant-based ingredients. In Mexico, tequila has been reported as a cause of oral allergy syndrome, hives and headaches.

Reports of reactions to cannabis, including anaphylaxis, are also emerging as the legalisation of recreational use spreads to more countries, and can happen when smoking weed or eating its seeds.

Cannabis can also worsen reactions to food, as in this case of a man with wheat-dependent exercise-induced anaphylaxis (WDEIA) who only suffered from reactions after also smoking cannabis.

Cannabis can also cause secondary food allergies; one of its allergens (a lipid transfer protein, Can s 3) can cross-react with the equivalent protein in a wide range of plant foods, including cereals, fruits and nuts—hence the relatively recently coined term ‘cannabis-fruit/vegetable syndrome‘ which has been applied to cases involving reactions to peach, apple, nuts, tomato and citrus fruits including orange and grapefruit—as well as tobacco, latex, wine, and beer.

Currently, these types of cross-reactions have only been reported in Europe, where people are more likely to become sensitised to LTP allergens, for reasons as yet unknown.

Another special mention: food additives

Food additives—such as colourings like carmine and tartarazine, preservatives like potassium metabisulphite (anti-browning agent) and benzoic acid (antimicrobial agent), stabilisers like xanthan gum and flavourings like ethyl vanillin—also seem to pose more problems for adults than for children.

They have been known to cause problems for a small proportion (0.01 to 0.2%) of the adult population since the 1980s, to both foods and medication and, although they can cause problems for children, most of the reports have been made in adults.

The reactions are said to be ‘pseudoallergic’, which means that they produce the same symptoms as classic IgE-mediated allergies—namely chronic hives, recurrent swelling (angio-oedema) and asthma—but they are not thought to be directly caused by the immune system. A ‘pseudo-allergy’ to food additives is generally diagnosed by eliminating them from the diet for a few weeks and then undergoing a food challenge with a meal rich in additives, although sometimes skin tests may be used.

A recent German study designed to examine the characteristics of adults with hypersensitivity to additives revealed that they had an average age of 45 years, that 4 in 5 were women, that they were less likely to have a history that include allergies or anaphylactic reactions than people with regular food allergies, but that they were more likely to suffer from diarrhoea. In contrast to other studies on the subject, this one found that the prevalence of skin symptoms like hives and swelling was quite low, affecting between 1 in 3 and 1 in 4 people. Preservatives and colouring agents were the most common instigators.

The researchers noted that confirmed food hypersensitivity to additives was rare but also probably under-diagnosed, and that food additives should be suspected as the cause of reactions in people who report symptoms to various (botanically) unrelated foods or certain commercially prepared foods, symptoms that cannot be confirmed with the usual IgE-focused allergy tests.

Adults with classic food allergy are more likely to be allergic to several foods than children, who are more likely to be mono-sensitised (react to one).

This has been highlighted in multiple studies, from a 1996 British study examining peanut and nut allergies which noted that ‘Multiple allergies appeared progressively with age’, to a 2023 study looking at multiple food allergies in Americans which revealed that just under half (46%) of all adults with convincing food allergies (i.e. with symptoms fitting a list of criteria put together by a panel of experts) reported multiple food allergies. Of those people, roughly 3 in 5 reported allergies to 2–3 different foods, and the rest, to more than 3, with the number of foods peaking between the ages of 18 to 49 before slightly decreasing again. According to another American study, adults with childhood-onset allergies are more likely to report multiple IgE-mediated food allergies than adults who only started to develop these allergies during adulthood.

On the other side of the world, researchers have recently reported that just over a quarter (26.7%) of Thai adults with food allergy are allergic to more than 2 foods from different food families—that is, they counted an allergy to, for example, shellfish and wheat as 2 separate allergies, but not an allergy to shrimp and crab.

And a South Korean study reported that over half (57.3%) of all food-allergic adults are allergic to multiple foods (on average, 2.39). In fact, allergy to multiple foods was one of the largest differences between food-allergic and adults and children. Fruit was the most common trigger category (with apples, peaches and plums being the most frequent offenders), followed by seafood (mainly crustaceans), grains, legumes, nuts and seeds.

Adults who suffer from a classic food allergy also experience different, often more severe, reactions than children.

In general, adults are more likely to experience systemic reactions—reactions that affect the whole body—than children, and these reactions are often more severe, especially in adults with asthma (2) or those who were younger (around 22) when they had their first reaction. A big part of this is due to the fact that adults with persistent childhood allergies tend to have the more severe versions.

The potential severity of reactions to food (and medicine) in adults was demonstrated way back in 1969 by an American team of researchers who described the characteristics of allergic reactions in 15 adults, 8 of whom had had recurrent anaphylactic reactions before the offending substance was identified.

Some foods are known to be more dangerous than others; milk, for example, is something that often (but not always) affect adults less severely than children when the allergy develops later on in life, with many adults being able to tolerate baked milk if not the unheated version.

By contrast, peanuts, tree nuts and shellfish tend to cause serious reactions in childhood and they keep on doing so in adulthood. In fact, they can provoke even worse reactions in adults, often ending in anaphylaxis including dizziness and/or loss of consciousness, especially if they are enduring childhood allergies. That said, allergies picked up in adulthood are frequently hazardous, (7) too; an adult’s first reaction to a new food trigger, especially seafood is often anaphylaxis.

Even in Mexico, where seafood is not a particularly popular menu item, the number of cases of allergy to shrimp is increasing, and researchers have noticed that shrimp is the most important cause of oral allergy syndrome, hives and anaphylaxis, which they think may indicate a process of sensitisation (reflected by increasingly serious symptoms) during the development of IgE-mediated allergies.

Local eating habits are important for shaping the prevalence of food allergies in different parts of the world. In Korea, for example, the most hazardous foods for adults are wheat and buckwheat, whereas allergies to egg, milk, fish or seafood are rare.

Another food that often provokes severe reactions in countries like Korea, China and other East Asian countries, but is unlikely to be seen as problematic in other parts of the world, is silkworm pupa (chrysalis). Soft-shelled turtle is also a popular delicacy in China and was reported to be the second most common cause of anaphylaxis in 2009. Other traditional foods unique to China and prone to causing severe reactions include cicada pupas, grasshoppers, locusts and the two-lined velvet hawkmoth (Clanis bilineata).

Whatever the food, a study of Thai hospital patients finds that adults are more likely to experience cardiovascular symptoms than children and almost twice as likely to have an anaphylactic reaction as their first reaction.

National surveys of Americans produce slightly different results. One study reports that adults with adult-onset food allergy are less likely to have a severe reaction than adults with persistent childhood allergies, but that adults who have both childhood allergies and adult-onset allergies are the most likely to have severe reactions. Another study reports that adults with adult-onset and childhood-onset peanut allergy both have similar histories of severe reactions.

Which all goes to show that, although the numbers change slightly depending on the population being examined, a significant number of adults with food allergy run the risk of severe reactions.

In fact, what American research also tells us is that, whether it’s a study of medical records or a survey of random Americans, around half of food-allergic adults tend to experience severe reactions. These numbers are corroborated by research from Germany which has also found that around half of adults with IgE-mediated food allergies experience severe reactions. And a survey of adults in 6 European countries reported that just under a quarter (23.8%) of those with allergies to priority foods had experienced respiratory or cardiovascular symptoms during reactions.

Research from America further reveals that, within the population of food-allergic adults, women are more likely to have severe reactions than men, as are black adults and adults with asthma or hay fever.

However, adults over the age of 50 are less likely to have severe reactions, although an older age at the time of diagnosis is linked with a higher risk of severe reactions, although this could simply be because older adults with severe reactions are more likely to seek a diagnosis.

Data from the European Anaphylaxis Registry show that elderly anaphylactic Europeans are more likely to have cardiovascular symptoms (because, old age) but they are also less likely to have severe reactions to food (when they do, wheat and hazelnuts top the list) than other things like insect venom and drugs (because, again, old age, as well as the higher likelihood of having underlying health conditions like lung and heart disease), which is corroborated by Australian data.

Finally, people who get food allergies during adulthood are likely to keep them.

Older adults with food allergies tend to have developed them during adulthood, implying that once developed, they do not go away. This is especially the case for shellfish allergy. American survey data from 2015-2016 revealed a prevalence of shellfish allergy of around 2.8% among 18- to 29-year-olds and 2.6% among people 60 years or older, which was a lower rate of decrease across the life span than observed for other food allergies.

But whether you’re allergic to shellfish, peanuts or milk, if you developed a new food allergy during adulthood, chances are that you’re hanging onto it, especially if you start off with high levels of IgE-antibodies.

The good news is, if you managed to avoid this ‘classic’ type of food allergy during childhood, you’re probably in the clear. But there are a few types of food allergy that you’re more likely to get as an adult.

Image by Luis Lopez on Pexels

Pollen Food Syndrome (PFS)

Pollen food syndrome is by far the most common type of adult-onset food allergy, and it’s the reason why adults are more likely to experience their first allergic reaction to fruit, vegetables and/or nuts than children.

A 2019 review of (English language) studies worldwide estimated a prevalence of pollen-food allergy somewhere between 13% and 58% in the general adult population.

Pollen food syndrome is a secondary allergy which occurs when someone—often a woman—develops a primary allergy to pollen and their immune system later mistakes similar proteins in plant foods for the proteins in the pollen that they are actually allergic to, and then proceeds to mount a defensive reaction against those plant foods.

Different trees and weeds tend to sensitise people to different types of pollen proteins. Those different pollen proteins are structurally similar to–and thus more likely to be mistaken for—proteins in different plant families. Because different trees and weeds are more common in in different parts of the world, the accompanying food allergies also show regional differences.

For example, allergies to plant food like celery, soy, apple and hazelnut are more common in northern and central Europe where birch trees are endemic, whereas allergies to peach and peanut (4) are more common in southern Europe, where you find more plane trees and mugwort.

In North America, where ragweed is indigenous, allergies to melon and banana are more common than they are in Europe, but in Japan, where there are lots of birch trees and alder trees, which are also in the birch family, people tend to have allergies to the same kinds of plants foods that cause problems in Europe.

People with pollen food syndrome typically report symptoms associated with oral allergy syndrome (OAS)—which is not the same thing as pollen food syndrome and typically limited to an itchy tongue and/or throat—when they eat raw fruits, nuts and/or vegetables. Because the allergens that cause PFS are often heat-sensitive and tend to be destroyed by cooking or digestion, the symptoms are typically mild and localised to the mouth area.

For example, a common pollen-food allergy is Europe is hazelnut allergy. One study which examined hazelnut allergy in 86 adults living in 3 centres (Copenhagen, Zurich and Milan), most of whom were allergic to birch pollen, gave its subjects oral food challenges. 67 of them had a positive challenge and 59 (88%) had OAS symptoms confined to the mouth. 3 people (4.5%) had oral and gastrointestinal symptoms, and 5 (7.5%) had oral and systemic symptoms.

So, often in cases of pollen food syndrome, foods that are known to cause dangerous reactions when they are primary (i.e. ‘classic’) food allergies, often cause mild symptoms. That said, even allergens that are considered ‘mostly harmless’, like the PR-proteins associated with birch-induced PFS, can be dangerous, and about 1 in 10 pollen food-associated reactions can be systemic and occasionally life-threatening.

One study of 415 Korean food-allergic adults, for example, reported that 155 (37.3%) of them had PFS and that, while 97 (62.9%) had mild symptoms, just over a third had initially visited the allergy clinic due to respiratory symptoms or systemic reactions, and 20 (12.9%) had experienced anaphylaxis.

Similarly, an a study of American adults with suspected melon allergy gave its subjects food challenges confirming that 19 (36%) were indeed allergic to melon. Although 14 (74%) had oral allergy symptoms, 2 (10.5%) experienced life-threatening reactions, including respiratory and cardiovascular symptoms.

These more dangerous reactions are more likely to occur when the food allergy is due to proteins that are not destroyed by heating or digestion, like lipid transfer proteins (LTPs) which are frequently associated with an allergy to mugwort pollen and more severe symptoms when eating fruit like peaches.

More severe reactions can also be caused by the presence of cofactors, notably pollen season, which has been observed to make things worse for PFS-sufferers in a range of countries from Canada to Japan. Eating (or drinking) large quantities of the trigger food at once is also likely to cause worse reactions and has repeatedly been flagged in cases involving soy-containing drinks.

Pollen food syndrome has also been shown to cause delayed reactions, specifically in birch-pollen allergic people with eczema. For instance, in one German study, 37 birch pollen-allergic adults with eczema and no history of immediate allergic reactions to food underwent food challenges with carrot, celery, apple and hazelnut. 17 of them noticed their eczema getting worse within 2 days of eating the food.

You can read (much) more on Pollen Food Syndrome, including how to minimise the chance of reactions, here.

Image by MART PRODUCTION on Pexels

Food-Dependent Exercise-Induced Anaphylaxis (FDEIA)

The most important cofactor when it comes to provoking reactions to food is exercise, which is why it has its own name: food-dependent exercise-induced anaphylaxis. Although FDEIA affects both adults and children, adults and adolescents make up the vast majority of the cases.

Exercise-induced reactions to food can be caused by pretty much any food you can think of, but they are often caused by wheat, so that particular type of condition has its own acronym: Wheat-dependent exercise-induced anaphylaxis (WDEIA).

That said, FDEIA is a bit of a misnomer; for a start, episodes of FDEIA don’t necessarily result in symptoms of anaphylaxis. Indeed, people with FDEIA often start off having mild symptoms before going on to suffer worse ones, and Chinese research has shown that many people with exercise-induced anaphylaxis to wheat tend to suffer from recurrent hives instead for months or even years in the run-up to their first anaphylactic attack.

Secondly, the ‘exercise’ in question can involve as little as a brisk walk or a bit of ironing. In fact, there doesn’t have to be any exercise at all, a person can simply eat a lot of their trigger food.

Thirdly, reactions that fall under the current umbrella term of ‘WDEIA’ also include reactions that don’t involve food; aspirin and/or alcohol can be enough to trigger reactions in some people.

All of which has led to some discussion as to what the condition should be called; maybe ‘augmentation factor–triggered food allergy’ or maybe wheat anaphylaxis dependent on augmentation (factors)—WANDA—or wheat allergy dependent on augmentation (factors)—WALDA—if it doesn’t involve anaphylaxis.

FDEIA is also complicated to diagnose because reactions can be difficult to reproduce. Some reactions only happen during menstruation, or in a warm environment, or when someone is lying face down in the cold.

Luckily, FDEIA can be managed by avoiding your triggers (if you know what they are..) and, if that doesn’t work, by stopping exercise as soon as you notice the relevant symptoms (which tends to stop them from getting worse) or pre-medicating (if your symptoms seem unavoidable).

You can read a lot more about Food-Dependent Exercise-Induced Anaphylaxis and how to manage it here.

Image by Akashni Weimers on Pexels

Alpha-Gal Syndrome (AGS)

There are 3 distinct forms of allergy to red meat; the primary, ‘classic’ kind (which tends to affect children), pork-cat syndrome, a cross-reactive allergy caused by sensitivity to cat dander and often seen in adolescents and young adults, and alpha-gal syndrome, which can affect people of all ages but overwhelmingly affects adults.

A 2021 review of 103 studies covering 236 patients in 20 different countries reported that, of the 229 patients whose age data was available, just 11 (4.6%) of them were 19 years old or younger. Among the adults, the number of cases rises steadily with the patient age group, peaking among those aged between 50 and 59—the average age of an alpha-gal allergic patient being just over 51—before steadily decreasing again. In people aged between 80 and 89, there were only 5 reported cases.

This probably has something to do with the fact that the people most at risk are those who spend a lot of time outside in greenery, like hikers, hunters and forestry workers. And the risk among the elderly differs in different countries with different cultural pastimes. In Korea, for example, the average age of someone with alpha-gal allergy is just over 70 years old.

Unlike most other adult-onset food allergies, the people who get alpha-gal allergy are often men. This may also have something to do with the traditionally masculine professions of those most at risk, as well as the traditionally masculine preference for red meat. Or it might not.

And that’s not the only thing that’s standout about this mostly adult-onset allergy; alpha-gal syndrome is a unique type of food allergy in several ways.

First, sensitisation is caused not by eating or breathing in food allergens, but by being bitten by hard-bodied ticks (and possibly by other parasites yet to be definitively identified). There are several species of tick that can cause the allergy and they vary according to where you find yourself in the world. In North America, where the condition was first described the major culprit tick species is Amblyomma americanum, aka the lone star tick, which can be found on East Coast and in the Midwest but is moving northwards and westwards, partly in response to climate change.

Outside of North America, the major hots spots include Australia (thanks to Ixodes holocyclus, aka the paralysis tick), Europe (thanks to Ixodes ricinus, aka the castor bean tick) and Japan (thanks to Haemaphysalis longicornis, aka the Asian longhorned tick, and Amblyomma testudinarium). Other ticks have been identified as the possible cause of reactions in other countries, such as Amblyomma variegatum (aka the tropical bont tick, Ivory Coast) and Amblyomma cajennense (Panama).

Another unique aspect of this food allergy is that it’s caused by sensitisation not to a protein, but to galactose-α-1,3-galactose—aka alpha-gal—which is a carbohydrate sugar attached to a protein (making it a glycoprotein), found in the saliva of certain ticks. People who are bitten by these ticks, especially those who are bitten several times, become sensitised to the alpha-gal which is also found in mammalian (red) meat.

The reactions it produces are typically IgE-mediated but, in another major difference to other IgE-mediated food allergies, symptoms normally occur after a delay of 2 to 6 hours (although the time taken for them to appear can range from minutes to 24 hours). Symptoms primarily consist of skin manifestations—often hives (urticaria)—and around half of the reactions are anaphylactic (something that older adults are more likely to experience). Gastrointestinal symptoms occur in around a third of cases and just under 1 in 5 people suffer from respiratory symptoms.

Not everyone who is bitten by a tick and sensitised to alpha-gal subsequently reports allergic reactions to red meat. And some people describe no reactions or mild reactions after eating red meat, but then have severe symptoms after eating the same amount of meat, cooked in the same way, on another day. This may be due to an absence of relevant cofactors like exercise or alcohol.

Alpha-gal syndrome doesn’t just provoke reactions to food. Anything with an association to red meat can be hazardous, such as gelatin-containing vaccines and other mammalian-related medications (e.g. heparin, cetuximab—a cancer-busting drug which is administered via infusion and provokes immediate reactions), as well as pancreatic enzyme replacement (e.g. pancrelipase), heart valves from pigs and, possibly, antivenom.

The only way to manage the allergy is by avoiding ticks, red meat and associated products. Doctors at an American allergy centre in North Carolina have noticed that 4 in 5 (80%) of their patients can get rid of their symptoms by avoiding red meat and associated products (broth, gravy, lard) and alpha-gal containing medications, a number which rises to 95% when people also avoid dairy products, heart-valve replacements and gelatin-containing vaccines.

IgE antibodies to alpha-gal have been shown to decrease over time which implies that some people may be able to tolerate red meat in their diets after avoiding ticks and red meat for a period of months or years.

At the North Carolina allergy centre mentioned above, between 1 and 10% of patients have been able to successfully reintroduce red meat into their diets. Those who can tolerate dairy products are more likely to be successful than those who have to take stricter avoidance measures.

Image by Vaibhav Jadhav on Pexels

Occupational allergies

The last type of IgE-mediated food-related allergies that are much more likely to affect adults than children are occupational allergies, simply by virtue of the fact that most people, at least publicly, frown on child labour.

Food allergies that you can develop on the job come in two main flavours: respiratory and contact. The respiratory ones involve breathing in food allergens in the air around you, and the contact allergies involve becoming sensitised through the skin because you spend so much time handling food.

The most common of the respiratory allergies is baker’s asthma which, as the name implies, is an allergy that produces respiratory symptoms—often hay fever-type symptoms which are later followed by asthma—and often affects bakers. By far the most common food allergen in these cases is wheat, but all types of cereal flours like corn, barley, rye and oats can end up provoking symptoms if enough allergens are breathed in. These days, the increasing popularity of legume-based flours is making cases of occupational asthma to lupin and soy more common.

Other food allergens less commonly involved in this type of allergy include egg and sesame. And It’s not just food allergens that are involved; yeast and enzymes, widely used in the baking industry to speed up the bread-making process, are a frequent cause of baker’s asthma.

It’s not just bakers who are affected; people who work in flour mills are just as likely to develop occupational asthma as well as, to a lesser extent, workers on farms and in pasta factories, cake and biscuit factories, pizza bakeries, restaurant kitchens, malt factories, animal feed plants and agricultural research centres.

And workers’ families can also develop respiratory allergies as they become sensitised to food allergens that the breadwinners bring home on their skin and their clothes. In extremely rare cases, baker’s asthma can also affect children whose parents take them along to their workplaces, as in the case of a 2-year-old boy who contracted the condition while spending time at his grandparents’ bakery where his mother worked.

The good news is that most people who develop baker’s asthma to wheat can still eat wheat without symptoms, although why this is so remains a mystery. It may have something to do with the route to sensitisation being breathing and not eating. This is not always so, as shown by the case of a Turkish baker who was eventually unable to eat bread after developing baker’s asthma to wheat flour, and the case of a Spanish worker who developed an allergy to barley while handling flours and feeds at his job and who eventually became allergic to beer. But these cases are rare.

Bakers aside, the demographic most likely to be affected by occupational respiratory allergy are actually seafood handlers. Although this type of allergy affects people who process fish, it’s far more common among people who process shellfish, notably crustaceans.

In fact, so many workers in the seafood industry suffer from respiratory problems because of occupational exposure to allergens generated during processing that the International Fishing Industry Safety & Health Conference put out a statement in 2019 recommending that better measures be taken to protect workers from atomised seafood.

Working with seafood also produces contact allergies among processing workers and restaurant workers most commonly, but anyone whose work involves a lot of contact with seafood, such as fishmongers, delivery drivers and dolphinarium workers will be affected.

Contact allergies are also experienced by people who work with cereals, too, such as bakers and cooks and they can also affect people who don’t work with wheat but cook with it regularly, like the case of a mother who made chapatti bread for her family every day after work.

In fact, contact allergies can affect anyone who works with any type of food closely and often enough, from chocolate candy workers to scientists working in research labs.

Similarly, working with and around animals has also proven problematic for people working with poultry, who can develop bird-egg syndrome, and nature is not always kind to people whose work leads them to develop alpha-gal syndrome, such as foresters, forest workers, hunters and field biologists.

Finally, people who come into contact with latex on a regular basis can develop an allergy to the rubber. These include, like healthcare workers, greenhouse workers, hairdressers, housekeepers, and people who work in latex doll manufacturing plants.

This is relevant because people who are allergic to latex are at risk of develop an allergy to fruit and veg, aka latex-fruit syndrome (and latex-food allergy syndrome), another cross-reacting allergy like pollen food syndrome, only this time without the pollen

The foods most frequently involved are chestnut, avocado, banana, and kiwi, although many others are involved, including papaya, peach, pineapple, passion fruit, fig, melon, mango, walnut, bell pepper, cassava, tomato and potato.

Symptoms of latex food allergy syndrome include all of the usual symptoms associated with IgE-mediated allergies, but anaphylaxis is quite frequent and can be the initial reaction.

Image by Change C.C on Pexels

Food protein-induced enterocolitis (FPIES)

FPIES is a mixed food allergy—largely non–IgE-mediated but sometimes involving IgE antibodies—characterised by inflammation that can affect the whole gastrointestinal tract. It typically affects infants and young children and is often triggered by the introduction of cow’s milk or soy formula in early infancy and solid foods in late infancy, like oats and rice in the US or seafood in Italy and Spain.

FPIES is often outgrown during childhood and was traditionally thought to affect only older children and adults who were unlucky enough to have a persistent disease. However, allergists have quite recently discovered that FPIES occurs ‘not just in children‘ and cases of adult-onset FPIES are increasingly being reported. American national survey data has put the prevalence of FPIES in adults at 0.22%, which is roughly just under half the prevalence estimated for children (0.51%).

There are 3 main differences between child-onset and adult-onset FPIES; the trigger foods, the typical patient and the typical symptoms.

Although some cases of adult-onset FPIES can be triggered by egg or milk, the vast majority are triggered by seafood, often shellfish. Although the majority of people are allergic to one food, allergies to more than one are not uncommon.

Whereas childhood-onset FPIES normally affects boys, the majority of people affected by adult-onset FPIES are women; one Spanish case review, for example, reported that 83.3% of their patients were women, and a Canadian one reported that 68.4% of their patients were female.

The symptoms of FPIES in adults are also different to those commonly seen in children. FPIES is categorised as either chronic or acute, according to the symptoms it presents. Chronic cases are much rarer and the very vast majority are found in infants. However, there have been recent reports of adults suffering from chronic FPIES to egg. Chronic FPIES in adults can be recognised by chronic vomiting and diarrhoea, as well as stomach pain and fatigue.

The acute version of FPIES is by far the most common, and it’s here that symptoms often differ (although, not always). Acute FPIES in children is characterised by copious projectile vomiting within 4 hours of eating shellfish accompanied by certain other signs (such as pallor, extreme lethargy, dehydration, diarrhoea, a trip to the hospital’s emergency department), but no (skin or respiratory) symptoms typically associated with allergy.

By contrast, adults with acute FPIES often tend to suffer from:

• stomach pain and cramps
• diarrhoea
• vomiting
• weight loss

Symptoms of adult FPIES to some foods also have a shorter onset; although children tend to experience a reaction within 4 hours of eating shellfish, symptoms in adults often start within half the time, although onset falls within a larger range—anything from 3 minutes to 6.5 hours—and they last, on average, for 9 and a half hours, with a range of less than a minute to over 48 hours.

Although symptoms in adult FPIES are generally milder than those suffered by children, some cases can result in anaphylaxis. In what may be the first case report of adult FPIES, a 53-year-old British man was referred to an allergist after several episodes of diarrhoea and vomiting which had initially looked like food poisoning, a common occurrence with seafood allergy. He was given a food challenge and ended up having to be given adrenaline to counteract his severe response to 54 grams of poached scallops.

One final difference between child and adult FPIES is that around one third of children with the condition also have IgE antibodies to the trigger food—so-called ‘atypical’ FPIES—whereas this has not yet been reported in adults (although this could just be because those cases have been missed).

Although not much research has been done into adult FPIES yet, the research that has been done finds that symptoms are ‘commonly persistent’. However, some patients will outgrow the condition, with one Spanish study that followed 107 patients for just over 6 years reporting that 18 (16.8%) outgrew their allergy in an average of 3.5 years.

Image by Amanda Hemphill on Pexels

Eosinophilic oesophagitis (EoE)

Eosinophilic esophagitis (EoE) is a non-IgE-mediated disease characterised by inflammation that affects the oesophagus (i.e. the ‘food tube’).

Eosinophilic oesophagitis used to be considered a childhood disease and extremely rare in adults, but this was refuted by a slew of studies carried out around a decade ago. For example, a Dutch analysis of data in a large national medical database reported that the highest number of new cases was seen in men aged 20 to 29. A Spanish study carried out a few years later using data from two hospitals located in a central region of Spain stated that EoE was ‘ highly prevalent in adults from central Spain, being diagnosed in one out of 2250 inhabitants older than 16 years of age.’ The average age of their patients was 29.4 years.

These investigations were closely followed by an American analysis of national medical data that revealed that the average age of an American patient with EoE was 33.5 years. A more recent analysis of 10 years’ worth of patient data in a Swedish hospital revealed that the average age of the patients they diagnosed with EoE was 48 years. In this patient group, just under 10% were children. 75% were men and cases of EoE in general were on the increase.

These last 2 features of EoE are commonly mentioned in EoE studies. In fact, cases of EoE are on the increase worldwide, according to a meta-analysis of studies covering 15 countries and 147,668 patients. This meta-analysis also confirmed that there are more adults than children with the disease (at a ratio of just under 8:5), more males than females (at a ratio of just over 10:3) and more cases in North America than Europe or Asia.

Although not all cases of eosinophilic oesophagitis are due to food allergy, the majority seem to be and, among those that are, milk, wheat/gluten and egg are the most common food triggers in both children and adults in the US, Spain and Australia, according to a 2018 meta-analysis of studies on the subject.

Most people just have one or two food triggers which is why therapy for this kind of condition often involves avoiding the 2 most common triggers (milk and wheat/gluten) then, if that doesn’t work, following a 4 food elimination diet (milk, wheat/gluten, eggs and legumes) and, if that doesn’t work, trying a 6 food elimination diet (milk, wheat/gluten, eggs, legumes, seafood and soy). This tend to reduce the symptoms and tissue damage in most people with eosinophilic oesophagitis.

Symptoms of eosinophilic oesophagitis are age-dependent. In infants, EoE provokes general symptoms of oesophageal difficulties such as gagging, vomiting, feeding difficulties and ‘failure to thrive’ (being small for their age).

Young and school-age children have symptoms that are indistinguishable from those associated with gastroesophageal reflux; abdominal pain, vomiting and an unpleasant taste in the back of the mouth due to regurgitating sour liquid.

Older children and adults are more likely to have trouble swallowing (dysphagia, especially common in the elderly), to get food lodged in their oesophagus (food impaction) and, less commonly, to suffer from heartburn (pyrosis).

In fact, many adults with EoE tend to come to doctors’ attention after ending up in hospital because of ‘food bolus obstruction/impaction’, which essentially means that a large lump of food has become lodged in their oesophagus. This probably happens after years of complaining about not being able to swallow food properly but not being diagnosed with EoE until they end up needing hospital care.

Although adults with EoE are less likely than children with EoE to have other allergies such as asthma, eczema or IgE-mediated food allergies, they are more likely to have complications associated with their condition, such as anaemia, hypothyroidism oesophageal strictures (the abnormal narrowing of the oesophagus often due to scar tissue) and perforations (holes), probably because it’s taken them longer to get a diagnosis.

Because eosinophilic oesophagitis is a chronic condition with little chance of resolution, older people who may have had the disease for a long time before being diagnosed tend to have a longer duration of symptoms and worse tissue damage.

Image by KamranAydinov on Freepik .

Image by Any Lane on Pexels