Oral allergy syndrome (pollen food syndrome): symptoms, foods and treatment

Allergy UK says avoidance of the foods that cause your reactions is most important, with no need to avoid foods that do not cause symptoms. You usually only need to avoid the food in its raw form. It suggests trying the food cooked, canned or microwaved, and checking whether different varieties are tolerated. Lightly cooked foods such as stir-fried vegetables, and nuts both raw and roasted, have been known to cause symptoms in some people.

For a mild reaction, stopping eating and drinking water may be all that is needed, and symptoms should settle within 30 minutes to an hour. If you are concerned or symptoms are unpleasant, a non-sedating antihistamine can be taken. Allergy UK also advises continuing any prescribed hay fever or asthma medicines, which helps keep symptoms under control, and keeping a food diary if you are unsure which foods are involved. Where a severe reaction is a possibility, a clinician may prescribe adrenaline.

Anaphylaxis UK says symptoms usually come on immediately after eating the raw food and are most commonly itching or tingling, though swelling may occur. Allergy UK says most people have mild symptoms that settle within an hour.

• Redness, mild swelling or itching of the lips, tongue, inside of the mouth, soft palate and ears.

• Itching and mild swelling of the throat.

• Occasionally abdominal pain, nausea and even vomiting if the oesophagus or stomach is affected.

• Sneezing, runny nose or eye symptoms from tiny amounts of the food entering the nose or eyes, including when peeling or preparing it.

• Rarely, difficulty swallowing or breathing, which needs immediate medical help.

In oral allergy syndrome the immune system mistakes proteins in certain plant foods for proteins in pollen. Allergy UK explains that many fruit, vegetables, nuts and cereals have a protein structure very similar to the pollens of trees, grasses and weeds, a process called cross-reactivity. After a person has become sensitised to airborne pollen by breathing it in, the immune system can also react to the food protein as if it were an allergen.

The name is a little confusing. Anaphylaxis UK says some professionals use oral allergy syndrome and pollen food syndrome interchangeably, although strictly speaking the two are not the same, and that it prefers “pollen food syndrome” for symptoms linked to pollen allergy that are limited to the mouth and throat. This guide uses both terms for the same everyday picture.

Allergy UK says the most common foods are apples, peaches, kiwi, hazelnuts and almonds, but almost any fruit, vegetable or nut can cause a reaction. Anaphylaxis UK adds raw fruits such as apricots, pears, cherries, plums, nectarines and tomatoes, and raw vegetables such as carrots and celery, with legumes, soya milk and certain nuts also involved.

In the UK the most common pollen is silver birch, which causes hay fever symptoms from the end of March until the end of May, according to Anaphylaxis UK. It says about three quarters of people sensitised to silver birch pollen also develop pollen food syndrome. Grass and weed pollens such as mugwort can also be responsible, and people sensitised to both birch and grass pollen may react to a wider range of foods.

Anaphylaxis UK says that on rare occasions more severe symptoms, such as difficulty in swallowing and breathing difficulties, can occur and that immediate medical help is needed. Allergy UK says not to rely on antihistamines or an asthma inhaler if a food allergic reaction affects your breathing or circulation, for example causing faintness.

Allergy UK lists factors that can increase the chance of a severe reaction: eating a large amount of the allergen quickly (for example nuts, soya milk, fresh juice and smoothies), having allergies to many plant foods, uncontrolled or reactive asthma, and reactions that happen after exercise or with certain medicines. Both charities advise seeing a GP if you have symptoms of a food allergy, because some plant food allergies unrelated to pollen can be more serious.

Allergy UK says a healthcare professional can often diagnose pollen food syndrome from the consultation without further testing. If the diagnosis is unclear they may suggest a blood test or skin prick testing, and because fruit and vegetable allergens are affected by processing, testing may involve prick testing with the fresh food itself.

Anaphylaxis UK adds that some GPs refer to an allergy clinic, and that skin prick and blood tests help build a picture but do not show how severe the allergy is. It warns that conditions with similar symptoms, such as lipid transfer protein allergy and latex-fruit syndrome, need to be distinguished, and that asthma is a major risk factor for more severe reactions.

Most cases are mild and, according to Allergy UK, can be diagnosed and managed in primary care. It says a small proportion of cases have severe or unusual symptoms and need specialist input and further investigation, and that referral to a dietitian should be considered if food avoidance has become widespread. Anaphylaxis UK says that, because allergy is a specialist subject, your GP may refer you to an allergy clinic.

Allergy tests are also available privately. Anaphylaxis UK says skin prick and blood tests help build a picture but do not show how severe an allergy is, so a test result on its own is not a substitute for clinical interpretation. If you pay for tests, share the results with your GP.