Why do certain raw foods make my mouth itch?

Q. Why does my mouth itch when I eat certain foods?

A. Oral allergy syndrome, also known as pollen-food allergy syndrome, is an allergy to certain fruits, vegetables, and nuts that causes itching, tingling, redness, or mild swelling of the mouth, lips and throat when the food is eaten raw.

For most patients, when the food is swallowed and digestion begins, gastric acid and digestive enzymes disrupt the protein and the symptoms promptly fade. Although more common in adults, OAS occurs in children, too.

The symptoms result from pollen-related proteins found in certain foods. Patients usually have allergies to pollen first and then develop OAS later. However, many patients with pollen allergies will not go on to develop any OAS symptoms.

Sometimes OAS symptoms occur with only one food, while at other times, there are reactions to multiple foods. Apples and bananas are two of the most common OAS culprits. Apples are in the same family as birch tree pollen, so when a patient experiences OAS with apples, the reaction may actually be related to tree pollen allergy. Similarly, bananas and ragweed are closely related.

Because the fruit and pollen cross-react, OAS symptoms may occur more often during and right after pollen season. For example, those with OAS to apples should avoid eating them during tree pollen season in the springtime and in early summer. In general:

Birch pollen allergy may be associated with reactions to apple, peach, pear, plum, cherry, carrot, celery, almond, hazelnut, and legumes.

Grass pollen allergy may be associated with reactions to melon, orange, white potato, tomato, and peanut.

Ragweed pollen allergy may be associated with reactions to banana, melon, cucumber, zucchini.

Cooking the offending fruit or vegetable usually resolves the issue; for some, peeling it means they can eat it raw. It's also important to note that non-plant foods such as cow's milk and egg do not cause OAS.

For most patients, symptoms of OAS are mild and resolve quickly without intervention. But if more severe symptoms such as hives, vomiting, or trouble breathing develop, seek medical attention right away.

The best way to prevent symptoms is to avoid the offending foods during and just after the cross-reacting pollen season. OAS is usually a lifelong condition, unless the patient is treated with immunotherapy (allergy shots) for the underlying pollen allergy.

Magee DeFelice, M.D., is chief of allergy and immunology at Nemours/Alfred I. du Pont Hospital for Children.