Oral Allergy Syndrome (OAS)

  • What is oral allergy syndrome?

    Oral allergy syndrome (OAS), a type of food allergy, is an allergic reaction that is confined to the lips, mouth and throat.

    OAS most commonly occurs in people with asthma or hay fever from tree pollen who eat fresh (raw) fruits or vegetables. Other pollen allergies may also trigger OAS. Adults appear to be more affected than children.

  • Causes

    Oral allergy syndrome is due to a cross-reactivity between plant proteins from pollen and fruits or vegetables. When a child or adult with pollen allergy eats a raw fruit or vegetable, the immune system sees the similarity and causes an allergic reaction.

    Interestingly, many patients with oral allergy syndrome can eat the same fruits or vegetables when they are cooked. The cooking process changes the protein enough that the immune system does not recognize the food as being the same as the pollen anymore.

    Sometimes foods in the same botanical family will also cause reactions. Examples are potato and carrot, parsley and celery, or apple and pear.

    Cross-reactivity

     
    PollenPotential Cross-reactive Foods
    RagweedBananas, melons (watermelon, cantaloupe, honeydew) zucchini, cucumber, dandelions, chamomile tea
    BirchApples, pears, peaches, apricots, cherries, plums, nectarines, prunes, kiwi, carrots, celery, potatoes, peppers, fennel, parsley, coriander, parsnips, hazelnuts, almonds, walnuts
    GrassPeaches, celery, melons, tomatoes, oranges
    MugwortCelery, apple, kiwi, peanut, fennel, carrots, parsley, coriander, sunflower, peppers
    AlderCelery, pears, apples, almonds, cherries, hazelnuts, peaches, parsley
    LatexBananas, avocado, kiwi, chestnut, papaya
  • Signs and symptoms

    Rapid onset of itching or swelling of the lips, mouth or throat are the most common symptoms of OAS. Other symptoms may include irritation of the gums, eyes or nose.

    Symptoms normally appear within minutes of eating the offending food. Symptoms are also often worse during the spring and fall pollen seasons.

  • Treatments

    In most cases, OAS does not require medical treatment. It is best to avoid the offending foods. Often just peeling or cooking the food will reduce the effects.

    At times, an antihistamine can effectively relieve the symptoms. In adults and children with severe recurrent OAS, immunotherapy (allergy shots) to the pollen have been useful.

     

    Reviewed by: Asthma Section
    Date: December 2003