Oral Allergy Syndrome

​Oral Allergy Syndrome

Oral Allergy Syndrome (OAS) also commonly known as pollen food syndrome, is a hypersensitivity reaction to plant-based foods such as raw fruits and vegetables causing oral symptoms only which are mild and self-limiting.  It typically presents in people who are sensitised to tree +/- grass pollen with many patients having a previous history of hay fever. The protein structure in some grass and tree pollens (commonly Birch pollen) is similar to that in some of the plant-based foods which confuses the immune system, resulting in cross reactivity. As the food is ingested in raw form, patients may experience mild irritation/itching of lips (lips can become swollen), mouth and throat immediately or soon afterwards. Symptoms should settle within 30 minutes to an hour with or without antihistamine. Such foods are often tolerated when cooked.

OAS can also include peanuts and tree nuts but differentiation from potential systemic allergy can be difficult.

Patient Advice

Reassure that this is mild allergy. Rare to develop severe symptoms.

Avoid trigger foods

Try trigger foods in well-cooked form

May take oral antihistamine if symptoms not settling

Common foods which may cause OAS  

Cherries	Peach	Plum	Pear	Nectarine	Strawberries
Melon	Apricots	Watermelon	Apple	Fennel	Parsley
Spices e.g. cumin	coriander	Tomato	Cucumber	Spinach	Celery
Potato	Carrot	Swiss chard	Honey	Wheat	Aubergine

NB: Only foods identified by the patient are to be avoided and not all the foods on the list.