Oral Allergy Syndrome

Oral allergy syndrome or OAS is an allergic reaction to certain (usually fresh) fruits, nuts, and vegetables that develops in hay fever sufferers. This reaction occurs because the immune system mistakes food proteins for pollen proteins. Another term used for this syndrome is "Pollen-Food Allergy." It is treated like any other allergy, with medications and avoidance of foods that trigger the reaction.

OAS sufferers may have a number of reactions that usually occur very rapidly, within minutes of eating a trigger food. The most common reaction is an itching or burning sensation in the lips, mouth and/or throat. Sometimes other reactions can be triggered in the eyes, nose, and skin. Swelling of the lips, tongue, and uvula and a sensation of tightness in the throat may be observed. Serious allergic reactions (anaphylaxis) are rare. Some people with OAS may experience vomiting, diarrhea, indigestion, or cramps if significant quantities of an offending food are eaten.

An OAS sufferer should avoid foods to which they are allergic. Peeling or cooking the foods has shown to reduce the effects of the allergy in the throat and mouth, but may not relieve reactions in the gastrointestinal tract. Antihistamines may also relieve the symptoms of the allergy. Persons with severe reactions may be advised by their doctor to carry injectable medication (such as an EpiPen®) to treat themselves if necessary. Allergy immunotherapy (allergy shots) has improved or cured OAS in many patients.

In OAS, the immune system produces antibodies that are capable of binding to both pollen proteins and certain highly similar food proteins. Consequently, the same immune system response can trigger allergy symptoms in two different situations: hay fever (in the presence of pollen) and oral allergy (in the presence of certain foods).

Cross Reactions
Allergies to a certain pollen are associated with OAS reactions to certain foods. For instance, an allergy to ragweed is associated with OAS reactions to banana, watermelon, cantaloupe, honeydew, zucchini, and cucumber. This does not mean that all sufferers of an allergy to ragweed will experience adverse effects from all or even any of these foods. Reactions may begin with one type of food and with reactions to others developing later. However, it should be noted that reaction to one or more foods in any given category does not necessarily mean a person is allergic to all foods in that group. Often well-cooked, canned, pasteurized or frozen food offenders cause little to no reaction due to denaturation (structural changes or bending) of the cross-reacting proteins. Some important cross-reacting groups are listed below:

  • Alder pollen: almonds, apples, celery, cherries, hazel nuts, peaches, pears, parsley
  • Birch pollen: almonds, apples, apricots, carrots, celery, cherries, chicory, coriander, fennel, fig, kiwifruit, nectarines, parsley, parsnips, peaches, pears, peppers, plums, potatoes, prunes, soy, wheat; Potential: hazel nuts, and walnuts
  • Grass pollen: fig, melons, tomatoes, oranges
  • Mugwort pollen: carrots, celery, coriander, fennel, parsley, peppers, sunflower
  • Ragweed pollen: banana, cantaloupe, cucumber, honey dew, watermelon, zucchini; Potential: Dandelions or chamomile tea
  • Possible cross-reactions (to any of the above): berries (strawberries, blueberries, raspberries, etc), citrus (oranges, lemons, etc), grapes, mango, figs, peanut, pineapple, pomegranates, watermelon