All About Oral Allergy Syndrome

According to the British Dietetic Association (BDA), Oral Allergy Syndrome (OAS) or Pollen-Food Syndrome (PFS) affects about 2% of the population of the UK. Most symptoms are mild and are triggered by consuming certain foods. This condition is associated with other plant-allergy conditions like hay fever. In this article, we’ll tell you everything we know about OAS and its effects. 

What is oral allergy syndrome?

Oral allergy syndrome is also called pollen-food syndrome. It is a reaction to some plant-based foods that causes irritation but mostly mild symptoms to the mouth, throat and lips when certain foods are eaten raw. 

OAS is classed as a food allergy that usually develops in adults who already suffer from seasonal pollen allergies like hay fever. It is mostly in people whose allergy is to tree pollen. Although OAS can happen all year round, it is much more common during the summer months when pollen levels are high. Symptoms usually occur minutes after eating a food. 

OAS usually only causes symptoms when raw foods are consumed as heat breaks down the chemicals that cause it. When you cook or process vegetables, fruit and nuts, people generally won’t have reactions. That said, light cooking like stir-frying, steaming or poaching might mean a reaction still happens. 

Thankfully, serious reactions are rare. At most, they’re irritating and unpleasant and the symptoms tend to fade after a few minutes. The allergens causing the reactions are broken down by digestive enzymes and saliva so the symptoms are usually only present for a few moments.

On rare occasions, individuals with OAS can have a severe allergic reaction like anaphylaxis but this will happen only in around 2% of those with OAS.

Who does oral allergy syndrome affect?

OAS is considered to be relatively common and it affects 1 in 50 people. It is usually the same people who are sensitive to tree pollen, grass pollen or weed pollen. The condition usually affects people with hay fever in the spring or summer but can also occur in those who don’t have it. 

The most common pollen that affects people with OAS is birch tree pollen and it is believed that around 75% of people who are allergic to birch pollen will have some sort of reaction on their tongue and lips from eating raw apples. This is considered to be OAS in a mild form. 

Lots of people who develop OAS will have previously had symptoms of hay fever like itching eyes and sneezing for a few years before they go on to develop it. This is mainly true if the hay fever symptoms last beyond May rather than just up to May. The reason for this is that those who only have hay fever symptoms in spring are probably only allergic to tree pollen. Those whose symptoms continue until summer are probably more likely to get OAS as they’ll be allergic to grass pollen as well. 

People with allergies to both tree and grass pollen are the ones whose OAS will be present with a wider variety of foods like fruits, vegetables, tree nuts and peanuts. When only tree pollen allergy is present, the range of foods causing OAS symptoms is narrower.

However, there is no definite way to know who is going to get OAS. 

How common is oral allergy syndrome?

Lots of people have oral allergy syndrome but won’t realise they have it as it isn’t often diagnosed. However, it is believed that 2% of people in the United Kingdom have it. It is much more common in adulthood but children and adolescents can develop it too.

What causes oral allergy syndrome?

Oral allergy syndrome is caused by a sensitivity to allergenic pollen proteins. A person who is allergic to these through their respiratory tract might also become allergic to heat-labile food proteins that cross-react with proteins from pollen. These occur naturally in vegetables and fruit. 

Symptoms occur when an affected individual eats particular nuts, vegetables or fruit. Some people only have allergy symptoms with one food in particular while for others, lots of foods cause symptoms.

Those with a tree pollen allergy might develop OAS to a variety of foods. Some with a grass pollen allergy might too. However, there are also individuals with reactions that don’t seem to have particular tree or grass pollen allergies. Sometimes, especially if the reaction is initiated by tropical foods, a latex allergy could be the cause. 

Thankfully, most of the allergenic proteins that cause OAS are destroyed with cooking. This means the symptoms only occur when raw foods are eaten. However, this isn’t the case with nuts and celery as these tend to cause reactions after cooking too. 

Common cross-reactions

Depending on the specific pollen causing the allergy, the food reactions will vary. For example, people who have an allergy to ragweed pollen (soft-stemmed weeds that are part of the daisy family) tend to have OAS reactions with:

• Banana
• Melon (cantaloupe, honeydew, watermelon)
• Courgette
• Kiwi
• Cucumber

This doesn’t mean that all people with ragweed pollen allergies will get OAS symptoms when they eat these foods, though. We’ll detail more examples further in this article.

The biology behind the reactions

Oral allergy syndrome is intriguing in that it depends on an intricate interplay between allergic pollen proteins and heat-labile foods. It is triggered by the presence of specific proteins found in pollen, which share structural similarities with proteins in certain raw vegetables, fruit and nuts. The reaction is caused by cross-reactivity, where the immune system recognises similar structures in different proteins. 

The immune systems of people with pollen allergies are sensitised to airborne invaders. When pollen levels are high, the immune system responds accordingly and mounts a defence. This produces specific antibodies to neutralise the perceived threat. However, these antibodies not only recognise the pollen proteins causing the allergy but similar proteins in raw foods. It’s just like mistaking a stranger for someone you know. 

This all comes down to the fact that both pollen and certain foods possess shared epitopes, which are small regions on their surface. In essence, OAS illustrates how our body’s immune system, designed to protect us from harm, can occasionally misinterpret harmless substances as threats. 

What are the signs and symptoms of oral allergy syndrome?

The symptoms of OAS will usually come on within a matter of minutes of eating a food that triggers them. Here are some possible symptoms:

• Itching or burning of the lips, mouth, ear canal and pharynx (the top section of the throat).
• Reactions in the eyes, skin or nose.
• Swelling of the tongue, lips and uvula (the fleshy extension at the back of the soft palate).
• A feeling of tightness in the throat.

If the person swallows the food and the stomach acids don’t destroy the allergen, they might experience a histamine reaction that causes vomiting, diarrhoea, indigestion or cramps. Rarely, OAS reactions can be severe and present with wheezing, hives, low blood pressure and even anaphylaxis.

What foods cause oral allergy syndrome?

Most people who have OAS will have one or two food sensitivities depending on the specific pollens they’re allergic to. Here are some cross-reactions and the foods that might cause symptoms:

• Birch pollen: apples, peaches, pears, carrots, cherries, celery, chicory, fennel, figs, hazelnuts, coriander, parsley, kiwi, parsnips, peppers, potatoes, plums, soy, strawberries, wheat, prunes, jackfruit, almonds, snow peas, radishes, mung bean sprouts, and possibly walnuts.
• Grass pollen: melons, tomatoes, figs, celery, peaches, oranges.
• Alder pollen: hazelnuts, peaches, apples, celery, cherries, almonds, strawberries, raspberries, parsley, pears.
• Ragweed pollen: banana, melons, green pepper, paprika, cucumber, sunflower seeds or oil, kiwi, echinacea, courgettes, honey, dandelions, artichokes.
• Mugwort pollen: celery, carrots, mustard.
• Rubber latex: apples, almonds, apricots, banana, avocado, cherry, dill, chestnuts, ginger, kiwis, mangoes, melon, papaya, oregano, passion fruit, pear, peach, plums, sage, tomatoes.
• Rye-grass pollen: peanut, melon, watermelon and tomatoes.

How is oral allergy syndrome diagnosed?

To be diagnosed with OAS, it’s likely that a person also has a family history of atopy or has atopy themselves. Atopy is a type of allergy when there is a hypersensitivity reaction like asthma or eczema, which occurs in a part of the body that doesn’t come into contact with an allergen. Other symptoms like hay fever will mean that a food allergy is suspected. However, because cooked or processed foods (pasteurised, canned, frozen) don’t give symptoms, it can delay a diagnosis. 

Oral food reactions are often self-diagnosed mistakenly as people presume they are caused by contaminants or pesticides. What’s more, other food reactions like intolerances to proteins or other naturally occurring chemicals like salicylates need to be considered and distinguished from OAS symptoms.

Tests for oral allergy syndrome

Lots of people don’t know they have oral allergy syndrome but if they experience tingling, pain or swelling when they eat certain raw foods, they should be encouraged to visit an allergy specialist. It is recommended to keep a food diary before seeking a diagnosis. 

Usually, the specialist will take a comprehensive history to narrow down which allergies to test for. Tests may include a skin prick test, blood tests, patch tests and even oral trials. 

Examinations

To confirm the presence of oral allergy syndrome, an individual might be required to consume the suspected food and then have their symptoms recorded during an observation period. 

How is oral allergy syndrome treated?

Oral allergy syndrome is treated like many allergies. Avoidance of the allergen is the main way of dealing with the issue. However, the symptoms will largely depend on the levels of pollen so pollen charts can be useful to many sufferers. 

Peeling and cooking also helps to eliminate the effects of OSA. However, strawberries, celery and nuts still tend to have the effect despite cooking or processing. 

Antihistamine treatment

Antihistamine is a drug that stops the physiological effects of histamine. When the body has an allergic reaction, histamine is produced, which gives you the symptoms of an allergic reaction. It is a chemical messenger involved in a range of physiological processes. Antihistamine relieves these symptoms because they block the actions of histamine. There are two types of antihistamines:

• First-generation: Diphenhydramine and chlorpheniramine. These cause drowsiness and are used for short-term relief.
• Second-generation: Cetirizine, fexofenadine, and loratadine. These are more suited to long-term use and don’t cause drowsiness.

Epinephrine (EpiPen)

Anyone who has had an anaphylactic reaction will likely carry an EpiPen, which contains an emergency dose of epinephrine. This is an emergency auto-injector that is a portable device designed for easy and quick administration during emergencies. They are designed to be easy enough to use without training. 

Oral steroids

Occasionally, oral steroids, also known as corticosteroids, are prescribed. These are anti-inflammatory medicines that reduce inflammation as they mimic the effects of hormones produced by the adrenal glands. They also have immunosuppressive properties. 

Immunotherapy

Some patients have been cured of OAS through allergy immunotherapy. This is also called ‘desensitisation’. It is a unique treatment for allergies and works to improve or cure symptoms. 

The most common type of immunotherapy is subcutaneous immunotherapy, which is given by injection. The injection contains purified extracts of the allergen. These are given in hospital at different intervals. Typically, this will be once a week until the maintenance dose is achieved. At this stage, the frequency will be less. 

Another type of immunotherapy is sublingual immunotherapy (SLIT), which is an alternative to the injections. SLIT involves a dose of the allergen as a spray or tablet under the tongue. 

Final thoughts: Managing oral allergy syndrome

Managing OAS can be achieved by avoiding raw foods that cause the symptoms. If foods cause symptoms when lightly cooked, they should also be avoided. However, if your symptoms go beyond the mouth and into the gut, you’ll also need to stop eating the foods that are cooked. If nuts cause OAS, then these should be avoided altogether as cooking with nuts doesn’t alter the allergen. 

Oral allergy syndrome is a lifelong condition but it is relatively harmless as long as you can avoid the vegetable, fruit and nuts that cause symptoms.