Celery Allergy; More of a Problem for Continental Europeans

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Although celery is not that popular in English-speaking countries, where the stalk version just tends to be used as a vehicle for cream cheese or peanut butter, it’s hugely popular in continental Europe where is it used liberally in all its forms—stalk, root, seeds and leaves. This is unfortunate for the relatively large number of adults who develop pollen food syndrome, because celery is one of the most common vegetables associated with that form of allergy and a small amount of it can provoke severe reactions. As well as being problematic for people with allergies, celery also contains molecules with photosensitising properties and it can cause nasty phototoxic skin reactions in any random person who comes in contact with too much of it before catching some UV rays.

And now for the details, which include:

What is an allergy to celery?

Celery (Apium graveolens) is a plant that belongs to the Apiaceae family. This family used to be called Umbelliferae, because the members have flowers that look like upside-down umbrellas. The genus name of the celery plant, Apium, is Latin for ‘bees’, and it was given this name because bees are attracted it.

Celery is a native of the temperate Mediterranean region and the Middle East, but is now grown all over the world. It’s a biennial plant, meaning that completes its life cycle over 2 years (like, for example, carrots and onions). During the first season, the stems, roots and leaves grow and, during the second, the white flowers bloom, producing fruits and seeds before the plant dies.

Celery was originally used as medicine by several traditional medicine systems—traditional Chinese medicine (TCM), Ayurveda and the Unani system of medicine —and as a flavouring by the ancient Romans and Greeks, who also used the leaves to crown the winners of some of their most prestigious Games. It started to be cultivated as a food in Italy and France in the 1600s and gradually spread through Western countries, finally making it over to the US in the 19^th century. In 1896, the town of Celeryville, Ohio, was founded by celery farmers.

These days, celery can be found in many suburban spice racks, fridges and juicers, partly thanks to the misinformation spread by Instagram influencers concerning its miracle healing properties.

Although it does have many health benefits, contrary to popular belief, celery is not a miracle cure-all, nor is it a “negative-calorie” food—a type of food that contains so few calories that your body expends more energy in breaking it down and absorbing its nutrients than it could ever extract from it. Negative calorie foods are not a thing.

People can eat celery in stalk, root, or leaf form, as well as using the seeds for their flavour, but these are not all parts of the same plant. They, in fact, come from 4 different varieties:

	Wild celery (Apium graveolens)	Also known as smallage, wild celery blooms with tiny white flowers which produce the seeds that we use as a spice. The plant itself is very bitter and rarely eaten, but it is the parent plant of the other varieties of cultivated celery.
	Stalk celery (Apium graveolens var. dulce)	Also known as stick celery, this variety has large stems, or stalks, and is the most popular variety in the UK and US.
	Celeriac (Apium graveolens var. rapaceum)	Also called root celery, this variety has a large tuber and is popular in Europe.
	Leaf celery (Apium graveolens var. secalinum)	This variety has large leaves and is popular in Asia (hence its alternative name, Chinese celery).

TThe 2 varieties of celery most commonly bought by Western consumers are the root and the stalk, which are consumed raw in salads and as part of crudités platters, or cooked in sauces, soups, and stews. The plant seeds (actually very small fruit) tend to be ground and mixed with salt to make ‘celery salt’, or combined with other spices to make a spice mixture which is a common ingredient in processed and pre-packaged food due to its aromatic flavour. Celery seed oil is also sometimes used as a food ingredient or in cosmetics.

Unfortunately, celery can cause allergic reactions in a small percentage people. This happens because their body’s immune system mistakes one or more harmless celery proteins (and/or carbohydrates) for toxic invaders and creates IgE antibodies against them. The next time they eat celery, the antibodies recognise the proteins (and/or the carbohydrates) and prompt a response from immune system cells. These, in turn, release a variety of chemicals into the bloodstream, including histamine, the chemical that is primarily responsible for the symptoms of allergy.

The first case of celery allergy was described in Zurich, Switzerland, in 1926. Celery allergy was later linked to mugwort pollen allergy, which led to the term ‘celery–mugwort–spice syndrome’ and, later still, linked to birch pollen allergy, forming a ‘Celery-birch-mugwort-association’.

Since then, it has been bothering people—particularly northern and central Europeans—on a regular basis. Allergic reactions to celeriac and celery seeds, especially when they are used in the form of celery salt, tend to be more severe than reactions to celery stalk and leaves, because they contain more allergens.

Identified allergens

The proteins (and occasionally carbohydrates) in a food that are capable of provoking allergic reactions are called allergens. Allergens are named using the first three letters of the genus—Apium—the first letter of the species—graveolens—and a number reflecting the order in which they were identified.

As of March 2026, 7 celery allergens have been added to the WHO/IUIS allergen database (the official, peer-reviewed database of allergens maintained by the World Health Organisation and International Union of Immunological Societies):

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How common is celery allergy?

A definitive diagnosis of allergy can currently only be established with a food challenge, but challenges are costly in terms of both time and resources, as well as potentially risky. So many prevalence studies measure sensitisation—using skin or blood test data—but sensitisation is not allergy. Being sensitised to something simply means that your immune system recognises it, but you may not actually react to it; in fact, many people don’t react to whatever it is they are sensitised to. Studies that use sensitisation data therefore tend to produce allergy prevalence numbers that are larger than they should be.

In a similar vein, studies that estimate allergy prevalence using questionnaires usually produce somewhat inflated numbers as people can self-report allergies that they do not actually have, although robust studies will use certain criteria to evaluate respondents’ answers and determine whether their symptoms suggest an allergy or not.

IgE-mediated allergy

There’s not a lot of research available on celery allergy. It seems to be more common on mainland Europe than it is anywhere else. A 2021 analysis of the global pattern of food anaphylaxis reported an estimated prevalence of celery allergy in European adults of 0.14% and in European children of 0.04%. It doesn’t seem to be an important allergen in any other region of the world (for which there is data).

A 2019 study carried out in adults in 6 European countries reported a prevalence of celery allergy ranging from 0.33% in Reykjavik (Iceland) and 0.24% in Zurich (Switzerland) to 0.07 in Łódź (Poland) and 0.03% in Utrecht (the Netherlands) and 0% in Athens (Greece) and Madrid (Spain).

A 2020 study of children from the same European centres reported that celery is one of the major plant food allergens in central and northern Europe, finding a prevalence of probable food allergy of 1.24% in Łódź, 0.14% in Zurich and 0% in the other centres.

The authors of the studies noted that the reason that the prevalence of probable allergy to foods like celery was lower in children than in adults in central and northern European countries was probably due to pollen exposure, notably to birch, which affects adults more than young children and regularly causes cross-reactive food allergies.

A 2001 study carried out to examine the prevalence of sensitisation to different food allergens in Germany reported that celery was the second most common food allergen, with 14.6% of the 1537 adults they tested being sensitised to it. About three quarters (73.1%) of the people with food allergies (people with a positive skin test and history of symptoms) also had hay fever.

Other research has put the prevalence of celery sensitisation in Europe between 2.8% and 11.1%, and a study in Taiwan has reported a sensitisation rate of 1.8%.

Celery allergy tends to produce more severe reactions in adults than it does in children, and it also seems to affect women more often than men. Although that could be because women are more likely to seek treatment than men, food allergy in adulthood tends to affect women more often, and you can read more about why that is here.

Non-IgE-mediated and mixed allergies

There’s even less research available on non-IgE-mediated forms of celery allergy. The only non-IgE-mediated condition that celery is currently associated with is atopic dermatitis (AD), aka allergic eczema, which I shall now just call eczema, (although, strictly-speaking, AD is the most common subtype of eczema).

About 2.6% of the global population is estimated to be affected by eczema, which is just over 204 million people. It’s a condition that’s more likely to affect young children and females, and food is thought to be a trigger in 20% to 30% of the cases, with the most common allergens being milk, egg, soy, wheat, peanut and fish.

Although food-triggered eczema affects children more than adults, quite a few adults still have the condition. The prevalence of food allergy in children with eczema is estimated to be somewhere in the range of 15% to 30% and the prevalence of food allergy in adults with eczema is thought by most experts to be between 1% and 3%, with between 9% and up to 24.5% of that number estimated to be new, adult-onset cases.

Adults with eczema tend to be allergic to different foods than young children; namely those which are cross-reactive with airborne allergens—like celery, carrots, hazelnuts and shellfish—and those which people tend to start eating when they’re older (such as fish, in Western countries).

Not everyone with eczema and celery allergy suffers from a worsening of their skin condition after eating celery.

When researchers from the Czech Republic looked at the medical records of 113 adults with eczema, they found that 24 (21.2%) had celery allergy; of those people, 5 (20.9%) had eczema that got worse after eating celery.

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Cross reactions to celery

Technically-speaking, a person can be allergic to celeryand another food (or foods, or aeroallergen(s)) either by cross-reactivity—the immune system mistakes the proteinin one allergen for aprotein with a similar structure inthe other—or by an independent sensitisation to each food and/or aeroallergen(a co-sensitisation or co-allergy), in which case the immune system has developed specific IgE antibodies against each allergen. It can be difficult to determine whether reactions are caused by cross-reactions or co-allergies,but the end result is the same; problems, problems.

Allergy to celery can be primary—caused by a reaction to the celery itself—or secondary, caused by a cross-reaction in people who are primarily allergic to pollen. The latter type is more common and generally less severe.

Sensitisation to celery is often associated with sensitisation to birch pollen and/or mugwort pollen, hence the term ‘birch–mugwort–celery syndrome’.

Secondary celery allergy is more likely to be caused by birch pollen in Northern and Central Europe and mugwort pollen allergy in Southern Europe.

This is because birch pollen is the dominant tree pollen in Northern and Central Europe, but is relatively rare in southern Europe. By contrast, mugwort, is widespread throughout the northern hemisphere. The main European species—Artemisia vulgaris, aka common mugwort—is very common in southern Europe, where there are also several other invasive species present, resulting in a longer pollen season with several peaks.

People who are allergic to mugwort pollen are more likely to react to stick celery and heated celery than those who are allergic to birch pollen, and more likely to have systemic reactions to celeriac.

People who are sensitised to celery and mugwort pollen are often also sensitised to ragweed pollen.

People who are allergic to celery are often sensitised to other members of the Apiaceae family, notably carrots and spices, including:

• Anise (or aniseed)
• Caraway seeds
• Chervil
• Coriander
• Cumin
• Dill
• Fennel
• Parsley

Other spices that are involved in ‘celery–carrot–mugwort–spice syndrome’ include paprika/bell pepper (Solanaceae family) and pepper (Piperaceae family) and, more rarely, onion and garlic.

Thanks to the similar structure of panallergens found in several pollens (notably birch and mugwort) and plant foods, people who are allergic to celery are also often sensitised or allergic to apples, hazelnuts, tomatoes. cucumber and watermelon. A cross-sensitisation has also been noticed between celery and hops in people with an allergy to hop pollen.

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Symptoms of celery allergy

Celery can provoke both IgE-mediated symptoms and non-IgE-mediated symptoms.

Immediate reactions to celery

Immediate allergic reactions are caused by IgE antibodies. These antibodies bind to certain immune system cells—mast cells and basophils—and trigger the release of histamine and other inflammatory chemicals that cause the characteristic symptoms of allergy. Immediate reactions are the most common type of allergic reaction to celery.

Reactions are different for different people, and they can also be different for the same person, varying in severity from episode to episode. They can be classified according to the organs they affect and include:

• Skin symptoms: eczema (atopic dermatitis), hives (urticaria), swelling of the face (angio-oedema) and/or tongue and/or throat and/or hands, redness (erythema), itchy skin (pruritus), oral allergy syndrome (OAS, commonly manifesting as ‘itchy’ or ‘burning’ symptoms often limited to the mouth, sometimes also swollen lips and cheeks)
• Breathing symptoms: blocked nose (nasal congestion), runny nose (allergic rhinitis), wheezing, difficulty breathing/shortness of breath (dyspnoea), persistent cough, hoarse voice
• Digestive (GI) symptoms: nausea, diarrhoea, vomiting, stomach pain
• Cardiovascular symptoms: low blood pressure (hypotension), rapid heart rate (tachycardia), loss of consciousness (syncope)
• Neurological symptoms: headaches, dizziness, blurred vision, anxiety, confusion, seizures, fatigue and malaise (aka ‘a feeling of impending doom’, which can occur during anaphylactic reactions)

In celery allergy, as in most cases of food allergy, skin symptoms predominate. When 24 celery-allergic Swiss adults were given food challenges, 12 experienced OAS—10 of whom experienced OAS as their only symptom—4 experienced hives, 3 developed swollen faces, 3 had itchy skin, 3 had flushed skin, 3 experienced conjunctivitis and 1, rhinoconjunctivitis, 3 developed GI symptoms, 2 had heartburn and 1 felt sick.

It’s also possible for people to develop symptoms to celery without eating it, like the person in this study who developed hay fever-like symptoms after inhaling the aroma of a celery drink.

Although the majority of those who react to celery are adults, most of whom have Pollen Food Syndrome (PFS) and experience oral allergy syndrome as their primary, often only, symptom, reactions to celery are quite often systemic—symptoms affect more than one organ system and are not limited to the area that has come into direct contact with the allergen. In a German study in which 22 people with celery allergy were given a food challenge, half of them developed systemic reactions.

People with celery allergy and pollen food syndrome can also experience quite severe symptoms; for example, a French study of 20 celery-allergic people who were also allergic to birch or mugwort pollen reported that eating celery caused 17 of them to suffer from hives and swelling, 8 to suffer from breathing problems and 3 to have anaphylactic attacks.

Anaphylaxis

In fact, celery can cause serious reactions, especially in European countries. A 2021 analysis of anaphylaxis patterns around the world identified celery as the trigger food provoking around 5% of all reported cases of anaphylaxis among European adults. This was a much higher incidence than would be expected considering the prevalence of celery allergy (0.14%) among European adults.

A 2020 analysis of anaphylaxis registry data from the West Pomeranian region in Poland reported that celery was the 3^rd most common cause of anaphylaxis and had caused 11% of all reported cases, and that it was the 5^th most common food trigger among children, coming right after the usual suspects (peanuts, egg, milk and tree nuts).

Analysis of anaphylaxis registry data from Germany, Austria and Switzerland reported celery as the 3^rd most common trigger food in 2016 among adults, and the 2^nd in 2014, having caused just over 30 adults to report to hospital, as well as around 5 children.

A 2004 study named celery the leading trigger of severe food-induced reactions in one Swiss canton.

Celery is also an important allergen in southern Europe. In France, where celery is widely used to make aromatic flavour bases like Mirepoix, a study involving 580 food-allergic patients that examined the influence of ‘hidden’ allergens in foods as a cause of severe allergic reactions reported celery as the most common cause of anaphylaxis, involved in almost a third (30%) of all reactions.

And just because you suffer from oral allergy syndrome to one type of food does not mean that you will experience the same, mild symptoms to another. A 2012 report describes the case of a 28-year-old Polish woman who was allergic to birch pollen (as well as pollen from alder and hazel trees, which belong to the same family as birch) and suffered from OAS when she ate apples. When she tried eating raw celery, she ended up in the emergency department of her local hospital suffering from a serious anaphylactic reaction which started some 15 minutes after eating the celery.

Don’t panic: To be clear, the official definition of anaphylaxis is probably not what you think it is.

This means that many of the cases of anaphylaxis reported in medical studies are not actually life-threatening—when dealing with an emergency, however, since it’s impossible to predict which reactions will become life-threatening, every case of anaphylaxis should be treated as if it is potentially deadly.

A 2023 analysis of anaphylaxis cases registered by specialised allergy centres in Europe and Brazil noted that, while almost two thirds of anaphylactic reactions to food in children was triggered by 5 foods, adults had a much larger range of triggers; 11 foods triggers were identified as provoking two thirds of their reactions, and celery was one of them.

Most cases (93%) of celery-induced anaphylaxis were registered in Germany, France, and Switzerland and almost all of the patients also had hay fever, leading the researchers to speculate that birch pollen may be primarily responsible for provoking the anaphylactic reactions (as it is the most common type of pollen sensitisation in that region, although mugwort pollen has also been associated with celery allergy in this region, it’s just less common).

Anaphylactic reactions to celery were generally not as bad as those triggered by other foods, with just under a third (31%) being registered as cases of severe anaphylaxis. Celery also triggered the lowest percentage of gastrointestinal symptoms, with just under 1 in 3 (31.2%) patients experiencing them.

Finally, unlike other triggers like peanut, celery elicited reactions after the consumption of a full meal or a regular portion size in most cases, with around 2 in 5 of the individuals who had a reaction being unaware that they had an allergy to celery in the first place.

A serious reaction to eating celery can also be provoked in combination with exercise; so-called Food Dependent Exercise-Induced Anaphylaxis (FDEIA). Symptoms of food-dependent exercise-induced anaphylaxis tend to vary depending on how long you’ve had the condition. In the beginning, you will often suffer milder symptoms, including:

• itchy skin (pruritus)
• diffuse warmth and/or flushing
• tingling in the extremities
• hives (urticaria)
• swelling (angio-oedema) of the face and/or throat and/or extremities (often the hands)
• profuse sweating
• sudden fatigue
• headaches

People with FDEIA often experience mild symptoms for months or even years before progressing onto more severe reactions. These include:

• wheezing
• a feeling of tightness in the chest
• shortness of breath due to tightening of the air passages of the lung (bronchospasm)
• a swollen throat (laryngeal oedema) that makes swallowing difficult (dysphagia) and/or can make your voice hoarse
• nausea
• stomach cramps
• diarrhoea

A full-blown case of anaphylaxis will result in cardiovascular symptoms, including:

• low blood pressure and feelings of dizziness or faintness
• anaphylactic shock and cardiovascular collapse—not enough blood gets to your organs and you lose consciousness

An American study of 3 people (all of whom were also allergic to a pollen) with celery-induced FDEIA with typical symptoms describes how the reactions occurred either after exercising (the more common manifestation of FDEAI) or before. The symptoms occurred between 2 to 15 minutes into the exercise in those with the more common manifestation of FDEIA, or almost as soon as the celery was eaten in the person whose FDEIA was triggered by exercising before eating. Symptoms lasted between 1 to 4 hours after the attack began.

Happily, by avoiding eating celery around exercise, all of them were able to avoid any further reactions.

Celery also causes contact allergies.

There are 2 main forms of contact allergy that you can get from touching celery; contact urticaria (CU) and protein contact dermatitis (PCD).

Allergic contact urticaria basically looks like hives; an itchy, a weal and flare reaction that occurs within 10 to 60 minutes of touching the food and disappears within 24 hours.

Protein contact dermatitis is a term for allergic (or non-allergic) eczema-like reactions to food proteins. It can be chronic or recurrent and tends to occur on the hands, wrists and arms with periods of intensified reactions when you can feel of itching or tingling a few minutes after contact with the food you’re allergic to.

Contact allergies to celery are often experienced by farmers and occupational food handlers because these allergies are more likely to develop when a person is continuously exposed to the allergen and to things that affect the integrity of their skin. These allergies can become quite severe and may stop some people from being able to keep working.

You don’t have to work with celery to suffer from contact reactions after coming into contact with it; some people can develop contact urticaria after eating celery.

Delayed reactions to celery

Delayed allergic reactions can occur hours or even days after exposure to an allergen, unlike IgE-mediated reactions that often happen within minutes. These reactions either involve diseases that rely on cell-mediated mechanisms (immune responses that do not rely on the production of IgE antibodies but instead involve the activation of T cells and macrophages which leads to inflammation and tissue damage) or by ‘mixed’ diseases that rely on both IgE- and cell-mediated mechanisms.

The most common form of delayed reaction to celery is eczema.

Eczema is a chronically relapsing inflammatory allergic condition that specifically affects the skin and looks like this. It’s classified as a ‘mixed’ form of allergy that can produce either immediate or delayed reactions that can occur up to 48 hours after eating a trigger food.

Only a minority of people with eczema seem to experience a worsening of their skin condition as a result of eating their trigger food. Many actually experience immediate symptoms of allergy; a 2021 study of Czech patients with eczema revealed that, among the 24 who were allergic to celery, 20 experienced oral allergy syndrome, 15 suffered from itchy skin, 5 from GI symptoms, 3 from hives and 1 from breathing difficulties. Only 5 experienced a worsening of their eczema.

Celery-induced eczema typically takes the form of a delayed reaction in which the skin condition is aggravated hours after eating, as illustrated by one study in which people with birch-pollen allergy were given food challenges with cooked celery and found that their skin condition worsened within the next 24 hours.

Because symptoms can be severe, if you do suspect that you’re allergic to celery, it’s important that you see your GP/family doctor and get a referral to an allergy clinic for further testing.

Threshold for reactions

Celery is a very potent allergen.

VITAL®, the Australian initiative for voluntary incidental trace allergen labelling, put out recalculated threshold doses for the ‘Big 14’ allergenic foods in 2020. Using a database containing datasets from studies carried out worldwide that used double-blind, placebo-controlled food challenges (DBPCFC), they calculated that the lowest threshold dose of protein that was needed to produce a reaction in 1% of the population alllergic to celery is 0.07 mg. (Note: in this case, the ‘population allergic to celery’ is 82 people who were given a DBPCFC) This is one of the lowest eliciting doses of the main allergenic foods.

5.9 mg was the dose needed to produce a response in 10% of the test subjects, and 180 mg was the dose needed to provoke a reaction in half of the test subjects.

Note: we’re talking about milligrams of celery protein. There’s about 0.7 g (700 mg) of protein in 100 g of raw celery, and a large stalk of celery is about 64 g, meaning that it contains around 448 mg of protein. So a sensitive person would only need 0.07/448 = 0.00016, or just over a 10 thousandth of a large celery stick to provoke a reaction, or in layman’s terms, a lick. (Strictly-speaking, you won’t be allergic to every protein allergen, and the protein allergens are also differently distributed in the celery, so it might take more than a lick, but not much more).

Celeriac has also shown itself to be more potent than some of the better known and more feared allergens. A 2014 study found that the estimated dose of celeriac protein needed to elicit objective reactions in 10% of a study population was 1.6 mg, compared to the 2.8 mg for peanut protein and 8.5 mg for hazelnut protein.

2 people in this study had subjective (oral allergy) symptoms at 3 μg (micrograms) and 30 μg of protein, or 0.003 and 0.03 milligrams, which was between 1000 and 100 times less than the amount of protein that elicited subjective symptoms in subjects allergic to peanut, making celery potentially more problematic for some individuals when it’s ‘hidden’ in processed foods.

Because the protein content of celery spice is proportionally higher—about 4.5 times more— than the protein content of raw celery, celery spice can trigger reactions at much lower doses. In one study, some subjects who were given food challenges and reacted to 700 mg of raw celery only needed 160 mg of celery spice to provoke a reaction. One of those people even had a systemic reaction (an itchy mouth, runny nose and flushed skin). Another subject also developed a swollen face at twice the amount (320 mg).

160 mg was actually the starting dose used for the challenge in this study, so it’s possible that the people who developed symptoms after eating this amount of celery spice might have developed symptoms with a lower dose.

Ultimately, the threshold dose needed to provoke symptoms varies widely between people. It also varies per person, depending on the circumstances around the meal.

Your threshold can be lowered and your allergic reactions worsened by things called ‘cofactors’. Cofactors include things like how much you eat and whether those ingredients have been cooked or processed, as well as exercise, anti-inflammatory drugs, alcohol, infection and stress.

Celery has been specifically implicated in several cases of food-dependent exercise-induced anaphylaxis (FDEIA).

Cofactors are thought to play a role in about 14% to 30% of all anaphylactic reactions.

A 2013 study carried out in Germany identified celery as the second most common cause of food-induced anaphylaxis, including in situations involving cofactors.

Please note: the amount of celery needed to provoke a reaction says nothing about how severe the reaction will be. And, even if your reactions have been mild in the past, that does not mean that they will continue to be mild.

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Diagnosing celery allergy

A diagnosis of celery allergy will primarily be based on your clinical history—a record of consistent symptoms following the consumption of celery or celery-containing foods. This will require you to provide your allergist with answers to questions about your general medical background (including any other allergies you may have, such as hay fever symptoms—especially relevant if you’re having cross-reactions to birch pollen—and relevant illnesses in your family) and your dietary history (what you ate to provoke your symptoms, what those symptoms were, how long they lasted, whether you had exercised or taken painkillers and many other details).

Your medical history determines what comes next; on the basis of your answers, the allergist will try to determine what type of allergy you have—a primary, immediate-type allergy, a cross-reactive allergy or a delayed-type allergy—or whether it could be something else, and this will determine the tests they ask for to come up with a diagnosis.

Diagnosing IgE-mediated reactions to celery

Skin tests

An IgE-mediated sensitisation to celery is typically confirmed by a skin prick test, which involves someone placing a small sample of celery extract onto your skin (generally the forearm of an adult/older child or the upper back of a young child) and pushing it through the top layer of skin by pricking it with a lancet. It takes about 15 minutes to see a reaction (or not).

This test is often carried out first because it is quick and simple to perform and gives rapid results, but it is generally used to rule out an allergy rather than to confirm one, because it has excellent negative predictive value—if the skin weal is under a certain size, you are highly unlikely to have an allergy—but poor positive predictive value—the skin weal has to be very large before an allergist can say with any kind of confidence that you probably have an allergy.

The accuracy of the skin prick test is limited by the fact that the processing of commercially-made allergen extracts tends to destroy the heat-sensitive allergens, namely those which people with a suspected pollen-associated food allergy react to. In such cases, someone could get a false negative result and be wrongly told that they are not allergic to celery. The detection rate of celery allergy using skin prick tests has been put around 53%.

One solution to this problem is the prick to prick test. This test is very similar to the skin prick test, except first the lancet is used to puncture fresh food and then it is used to prick your skin. When the food is in liquid form, the technique is actually the same as the one used for the skin prick test and, when the food is solid, it’s often ground down and put in saline solution.

The prick to prick test often produces superior results to commercial extracts because the fresh food used should contain all of the allergens that a person can react to. The lab used by the clinic can also prepare the extract in specific ways which may add to its efficacy.

In one study, researchers gathered the skin test results of celery-allergic individuals from one clinic in Switzerland and one in France. In Switzerland, all 24 patients with celery allergy reacted to skin prick tests carried out with both commercial celery extract and fresh celery but, in France, 11 of the 12 celery-allergic individuals reacted to skin prick test with fresh celery, and only 3 of them reacted positively to the commercial celery extract. This shows both that all celery extracts are not created equal, and that you can be allergic to something and still have negative skin tests.

Blood tests

Sometimes, the doctor may decide to order a blood test, aka an immunoassay. Perhaps the skin prick test was inconclusive, or the suspected allergen is not available for skin prick testing, or you’re unable to undergo the test for some reason.

A blood test involves having a small sample of blood drawn so that it can be sent to a lab where technicians will use allergen extracts to check whether there are IgE antibodies in your blood that react to them. It can take 1 or 2 weeks to get the results.

Blood tests can be less sensitive or specific than skin tests, but they have other advantages: they are perfect for people who cannot stop taking certain medications or have extensive skin disease or tattoos, and they can safely be used on infants, squirming toddlers and people who are at risk of suffering an anaphylactic reaction.

Blood test panels also typically include a whole range of potential allergen extracts including other foods or aeroallergens that the allergist may want to check your reaction to.

For more specific information, a component blood test—aka Component Resolved Diagnosis (CRD)—can be carried out. Instead of using extracts of whole foods containing only (heat-stable, plentiful) allergens, the CRD tests the reaction of IgE antibodies in your blood to isolated, individual proteins. This improves the diagnostic sensitivity of the test as allergens that would otherwise be missing from the whole celery extract or exist only in tiny amounts are present in concentrated form in the CRD test.

This type of test enables the doctor to see exactly which allergen(s) you react to, which allows them to determine whether you are sensitised to cross-reactive allergens that are unlikely to produce symptoms, and whether you are sensitised to certain allergens that could affect your management plan. For example, if you’re mono-sensitised to Api g 2, you may be able to tolerate celeriac and only have to avoid stalk celery.

Component blood tests are also made up of very large panels of allergens which include many other foods and aerollergens that the allergist may want to check your reaction to and can help to determine whether or not a sensitisation to a cross-reactive allergen will be symptomatic or not.

Unfortunately, although CRD could potentially reduce the need for oral food challenges and contribute to tailored management plans, it’s not yet considered a routine diagnostic method and it’s not comprehensive; the most widely used tests neither contain all of the identified allergens (which are also not all of the possible allergens), nor are they universally available. Testing for certain specific celery allergens would require special preparation and is therefore only likely to be done for research purposes.

Additionally, as it is with skin and standard blood tests, CRD is better at confirming an allergy than at eliminating the possibility of one. And, because sensitisation patterns differ according to geography and populations—for example, adults living in northern or central Europe would recognise different celery allergens than adults from southern Europe—allergists need to understand their patient populations so that they interpret the results of the tests correctly.

A positive skin or blood test does not mean that you are allergic to something.

While lab tests do help with diagnosis, positive results only show sensitisation to specific allergens. Being sensitised to a food doesn’t mean that you’re allergic to it and that you will develop any symptoms. In this study, for example, 16 of 35 patients who had a positive skin test did not have any symptoms at all.

A positive test result simply means that your immune system is specifically aware of an allergen or allergens in that food. Why some people later develop an allergy to that food, and some do not, remains unexplained.

Neither can the results of your blood or skin test predict how severe your reaction to eating some celery might be; a large skin weal or high level of IgE in your blood do not mean that you will have a serious reaction if you accidentally eat some stew with hidden celery in it.

Likewise, some people who have negative blood test results still develop symptoms during an oral food challenge, like 5 of 22 people in this study. This can happen when a specific type of allergen that a person is allergic to is present in very low amounts in celery and, therefore, in the celery extract, like Api g 7.

Food challenge

The only way to get a definitive diagnosis of celery allergy, and to have some idea of how severe your reactions may be and how much celery is needed to provoke them, is to undergo an oral food challenge. This generally involves eating a very small amount of celery, waiting for a reaction, and then doing it again, gradually increasing the dose until an objective—visible—reaction occurs or a maximum dosage is reached. It can take around 4 hours, depending on the type of challenge undertaken and the length of observation time needed.

You can read more about oral food challenges here.

Oral food challenges are generally undertaken either when someone’s history and their test results disagree (i.e. they have negative tests results but their history strongly suggests an allergy, or vice versa) or to check whether someone has outgrown their allergy to ensure that they don’t unnecessarily restrict their diet or worry about hidden allergens in processed foods.

The former is well illustrated by a report which describes the case of a 41-year-old, mugwort-allergic Polish woman who was referred to an allergy clinic after suffering from several episodes of breathing problems after eating a mix of spices containing celery.

Her skin tests to several foods including celery were negative, as was her component blood test results (because they did not contain the specific celery allergen that she reacted to). The woman was understandably upset that there was no objective confirmation to explain her symptoms and so she underwent a challenge to celery. The challenge was discontinued after the suffered from subjective symptoms (itching in the mouth) which were later followed by objective symptoms (a runny nose and wheezing). She was given adrenaline, the advice to avoid eating celery and, importantly, both peace of mind and validation.

Because of the risk of severe reactions, oral food challenges should only be done by an experienced consultant in a medical setting.

Practically speaking, most people do not undergo this kind of test since it requires a lot of time and resources. And oral challenges are rarely, if ever, offered to people whose history includes severe reactions to a suspected food. Whenever possible, allergy diagnoses are based on a combination of medical history and lab tests.

Although food challenges help to diagnose food allergies and identify a suspect food, there are other reasons to undergo food challenges, namely:

• to identify culprit foods in cases of allergies to multiple unknown foods
• to determine a patient’s threshold—how much celery they can eat without reacting—so that dietary advice based on the outcome of the challenge can be given
• to confirm the development of tolerance to celery

Diagnosing non IgE-mediated and mixed reactions to celery

Non IgE-mediated diseases are difficult to diagnose for several reasons, not least of which is the fact that IgE testing is often of no use.

Skin tests

Eczema is diagnosed based on personal and family history of allergy and a skin examination. While there are no standard diagnostic criteria, there are certain features that a doctor can look for to diagnose it.

That said, these criteria are based on the characteristics of paediatric eczema, which is not the same as the manifestation of eczema in adolescents or adults, making diagnosis of eczema in older age groups more challenging. Sometimes people with eczema in these age groups will have to undergo additional tests to rule out other diseases first, and a skin biopsy may be needed before a diagnosis of eczema is made. However, these differences are now being taken into account and guidelines are being updated.

Once the diagnosis of eczema is made, efforts will first be made to try and get the skin condition under control using topical skin creams and drugs before any further testing is done. Generally, only if the skin is not getting any better will tests be carried out to see whether allergens, like food, could be aggravating the condition.

The identification of potential food allergens is generally done by looking for specific IgE antibodies to a food using skin prick tests or blood tests (the latter is often used if the skin condition is too bad for a skin test, or medications are being taken that will interfere with the results, or if the tests involve a young infant).

In cases of delayed symptoms, doctors may use the atopy patch test (APT). This test generally involves walking around with food (either fresh or in solution) contained in tiny aluminium capsules taped to your back for up to 3 days and having your skin checked for a reaction after 48 hours and 72 hours.

A skin application food test (SAFT) may be used instead for children under the age of 4. It’s basically the same thing, but the capsule of food is only applied to the skin for 10 to 30 minutes. It’s had mixed results, having been described as reliable and child-friendl and also as not being as good as the APT in diagnosing certain food allergies.

Elimination diets and food challenges

While skin tests may provide an indication of sensitisation, they cannot diagnose a food allergy; that has to be done with a food challenge during which the doctor can see whether or not, in addition to the immediate reactions, the suspected food also produces a worsening of the skin symptoms within the next 48 hours (often within a day). If it does, the food can then be eliminated from a person’s diet and their skin condition will be monitored for the next few months to see if there is a persistent improvement. When more than one food is suspected, the next challenge will be done a few weeks after the first one.

Image by Daniela Paola Alchapar on Unsplash

Image by Jakub Żerdzicki on Unsplash

Good to know

Immunotherapy for celery allergy is still a long way off.

In the 1990s, a few attempts were made to see if pollen immunotherapy would help to reduce the symptoms provoked by pollen-related food allergy. Though initial results were promising, a study carried out in 2006 concluded that birch pollen immunotherapy was not able to ‘alter the immune response to pollen-related food allergens’.

A recent Polish case report of anaphylaxis to celery in a woman who had completed a course of immunotherapy to birch and grass pollen a couple of weeks previously demonstrates that, in her case at least, treatment for an allergy to birch pollen did not get rid of the celery allergy.

However, there has also been a recorded success involving immunotherapy to celery itself: a 49-year-old woman with a severe celery allergy was given 0.1 ml of a commercial natural celery juice five times a day for 3 months and was able to tolerate 10 g of raw celery although she developed flushing to 20 g, however, she continued to ingest 25 ml of raw celery juice for 3 years and did not have any further episodes of anaphylaxis (that we know of).

Not all varieties of celery are created equal.

A study assessing the clinical reactivity of different celery cultivars—varieties produced by selective breeding—found that the celeriac cultivar ‘Anita’ is better tolerated in allergic patients than the ‘Prinz’ one.

Celery can also be hazardous for people who are not allergic to it.

Celery is a member of the Apiaceae family, a generally hazardous species that includes several plants that are known to be poisonous to humans, like hemlock. But its most problematic plants are those that cause phytotoxic reactions—namely phytophotodermatitis (PPD)—due to their high concentration of furocoumarins, photoactive compounds whose function is to stop fungi from harming the plants.

Phytophotodermatitis is a reaction that occurs after a person’s skin is first smeared with the plant’s natural photosensitising chemicals—chemicals which make your skin more sensitive to sunlight—present in the sap and fruits, and then exposed to UV light. This causes the skin to become acutely red and often to blister, typically between 12 and 36 hours after exposure to the UV light. The affected area then tends to develop traces of hyperpigmentation 7 to 10 days after the rash, and this can last for years.

Phytophotodermatitis is not an immunologic reaction, meaning that it can affect anyone who has a lot of contact with celery—particularly the root (celeriac), which contains the greatest concentration of psoralens (a type of furanocoumarin)—and is then exposed to lots of UV light, which can come in many forms; from the sun, from tanning beds—a particular risky activity as they produce concentrated UV light—or from undergoing UV therapy (PUVA) for other skin conditions.

Over the years, celery has been responsible for ‘outbreaks’ of rashes among celery harvesters, market gardeners and grocery shop workers who come into regular contact with celery and then either spend a lot of time in the sun or use a tanning bed. This is even more likely to happen if the celery has pink rot, i.e. is infected by Sclerotinia sclerotiorum, a fungus that causes the celery plant to produce more furanocoumarins.

You don’t have to work with celery to be at risk of these types of reactions, either, sometimes you just have to eat a lot of it, and then spend a lot of time in the sun, or undergo UV therapy or spend some time under a sunbed.

Prevention remains the best form of treatment—if you’ve had a lot of contact with celery, wash your hands and arms with soap and water and change your clothes, and avoid exposure to lots of UV light afterwards. And if you’re not a farmer of grocer, don’t eat lots of celery and then try to get a suntan.

Photo by jason roy on Unsplash