Oral allergy syndrome (OAS) is an allergy to one or more usually fresh fruits or vegetables. It is a common food-related allergy in adults and is increasingly diagnosed in older children. Symptoms are often confined to the mouth and develop within a few minutes of eating the food. The allergy is to proteins in the fruit that are similar to those found in tree (especially birch tree), grass or weed pollens causing hay fever.
Itchiness or tingling in the lips and mouth. Sometimes local swelling of lips and tongue “angioedema”. Less commonly urticaria (nettle rash), wheeze or abdominal pain may occur.
Unlike other food allergies, symptoms in OAS are usually limited to the mouth, lips, tongue and throat because the proteins causing the allergic reaction are broken down by saliva and digestive juices in the stomach. Cooking the food also destroys the proteins. People with OAS may therefore be able to eat cooked fruit such as apple pie but react to raw apples. Processed foods e.g. jam, and canned fruits are also often tolerated.
Most people with OAS react to only 1 – 2 foods, although some may develop allergy symptoms to a number of foods. There is presently no way to predict who will develop a problem to a particular food.
|Pollens||Fruit and Vegetables||Nuts||Other foods|
|Tree pollens (Alder & Birch)||Apple Cherry Carrot Peach Peas & Beans Pear Plum Potato Strawberry Tomato||Almonds Hazelnuts Walnuts||Coriander Fennel Parsley Peanut Soyabean Sunflower|
|Grass pollen||Kiwi Melon Peas Potato Tomato||Peanut|
|Mugwood||Apples Carrot Celery Melon Onion Peach Pepper Tomato||Basel Dill Fennel Mustard Oregano Parsley Pepper Thyme|
Skin tests to pollens may be considered if there are hay fever symptoms (sneezing, itchy / runny nose and eyes). There is often no reaction to standard skin testing solutions as the proteins (allergens) are destroyed in the process of producing the test solutions, just as they are in cooking. Skin testing using the fresh food is more reliable.
Foods can be safely tested at home by touching a little of the fresh food to the lip. If there is no tingling, itchiness or swelling then a bite may be taken, the food chewed and spat out. If the patient is allergic symptoms should occur within 15 minutes. If symptoms included swelling, wheeze or abdominal pain then test foods only after seeking medical advice.
Raw foods causing troublesome symptoms should be avoided. Lightly cooked foods, e.g. dishes which include stir fried vegetables or steamed / poached fruits or vegetables are usually tolerated, but if they also cause a reaction, they should also be avoided. If symptoms are more extensive and not confined to the mouth, specialist advice should be sought.
Symptoms usually respond to rinsing the mouth and then taking a dose of antihistamine. As anaphylaxis (severe allergic reaction) is unlikely, injectable adrenaline devices are not usually necessary.
If hay fever symptoms are particularly troublesome and not controlled with standard medication, further medical advice should be sought as other treatments might be considered.