Oral allergy syndrome

What is oral allergy syndrome?

Oral allergy syndrome refers to oropharyngeal symptoms triggered by eating specific raw foods.

As it occurs in people with pollen allergy, oral allergy syndrome is also known as pollen-food syndrome.

Who gets oral allergy syndrome?

Oral allergy syndrome affects older children and adults who have pollen allergies, which are common causes of hay fever and atopic asthma. It is not common for younger children or babies to develop oral allergy syndrome.

• Grass pollen allergy may be associated with oral allergy syndrome to raw orange, kiwifruit, tomato, melon, watermelon, potato and peanut.
• Birch pollen allergy may be associated with oral allergy syndrome to raw apple, kiwifruit, tomato, nectarine, apricot, pear, plum, prune, cherry, carrot, celery, parsnip, potato, parsley, dill, coriander, green capsicum, peas, lentils, beans, peanut, hazelnut, walnut, almond and sunflower seeds.
• Ragweed pollen may be associated with oral allergy syndrome to raw banana, cucumber, courgette, melon and sunflower seeds.

Grass pollen

Birch pollen

Ragweed pollen

What causes oral allergy syndrome?

Oral allergy syndrome is caused by cross-reactivity of an IgE mediated ('immediate') immune reaction to specific proteins which are found in inhaled allergens (pollens) with a similar protein which is found in some raw fruit and vegetables. Cooking these foods alters the protein so that most people with oral allergy syndrome are symptom-free with cooked foods.

It is unclear why some people with pollen allergies develop oral allergy syndrome whilst many do not.

What are the clinical features of oral allergy syndrome? 

Oral allergy syndrome can affect the mouth, tongue, ears and/or throat.

• Itching, redness or swelling occur soon after eating certain raw fruit and vegetables.
• Other symptoms may include throat pain, nausea, sneezing, runny nose and eyes, and swelling around the eyes.
• The reaction usually occurs immediately after eating the trigger food but symptoms can evolve over more than an hour.
• Symptoms usually settle within an hour of onset.

What are the complications of oral allergy syndrome?

Oral allergy syndrome usually settles quickly without complications. If symptoms spread beyond the mouth area after eating raw fruit or vegetables, medical advice should be sought. In the rare cases where the breathing is affected, although it is not likely to be serious, immediate medical attention is necessary.

A small proportion of patients with oral allergy syndrome develop systemic symptoms or anaphylaxis.

How is oral allergy syndrome diagnosed?

Oral allergy syndrome may be diagnosed by a specialist in oral medicine, allergy or dermatology based on the clinical history.

Blood tests (for specific IgE) and skin prick testing to fresh foods can be helpful in some cases but these tests alone do not diagnose oral allergy syndrome and referral to a specialist clinic is required. Commercial extracts are usually not suitable for skin prick testing for oral allergy syndrome because the protein allergens are typically unstable and may be altered during the extraction process.

What is the differential diagnosis for oral allergy syndrome?

• Allergic contact dermatitis / contact stomatitis / contact cheilitis
• Irritant contact dermatitis, such as lip licker's dermatitis
• Contact urticaria
• Angioedema and anaphylaxis
• Oral lichen planus
• Other mouth disorders 
• Gastrooesophageal reflux disease
• Eosinophilic oesophagiitis

What is the treatment for oral allergy syndrome?

People with oral allergy syndrome are advised to avoid the raw foods which trigger their symptoms. Only the foods associated with symptoms need to be avoided. Most people with oral allergy syndrome are able to eat cooked forms of the same foods without triggering symptoms.

In case of accidental ingestion of the trigger foods, symptoms of oral allergy syndrome usually quickly subside once the food is swallowed or removed from the mouth and usually no treatment is needed. Rinsing the mouth with water may help to reduce symptoms. If symptoms persist, an antihistamine tablet may be helpful.

Immunotherapy to pollens may reduce symptoms for a small proportion of patients although this is usually not recommended.