Definitions

total allergy syndrome

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. OAS is a food allergy: the immune system mistakes the food proteins for pollen proteins and causes an allergic reaction to the food. Another term used for this syndrome is '"Pollen-Food Allergy."'

It is treated like any other allergy, with medications and avoidance of anything that triggers a reaction.

Symptoms

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 pharynx. 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. Seldom it can result in anaphylaxis. If a sufferer swallows the food, there is a good chance that there will be a reaction later in the gastrointestinal tract. Vomiting, diarrhea, severe indigestion, or cramps may occur.

Treatment

An OAS sufferer should avoid foods to which they are allergic. Peeling or cooking the foods has shown to eliminate the effects of some allergens such as apple, but not others such as celery or strawberry. In the case of foods such as hazelnut which have more than one allergen the effects can be mixed - eliminating one but not the other. Antihistamines may also relieve the symptoms of the allergy by blocking the immune pathway. Persons with a history of severe anaphylactic reaction may carry injectable emergence dose of epinephrin (such as an EpiPen). Allergy immunotherapy has been reported to improve or cure OAS in some patients. A year-long study ending in 2004 indicated that immunotherapy with extracts containing birch pollen has benefit to OAS sufferers of apple or hazelnut related to birch pollen-allergens. Even still, the increase in the amount of apple/hazelnut tolerated was still small (from 12.6 to 32.6 g apple), and as a result, a patient's management of OAS would be limited.

Mechanism

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 food allergy (in the presence of certain foods).

The antibody may react to the linear (amino acid) sequence of the protein or to a conformational epitope. If the response is to the conformational epitope, then the person with OAS may be able to eat the food when it is cooked, but not when it is raw. If the response is to the linear sequence (common in tree pollen/nut allergies), then cooking the food has no effect on its ability to trigger an allergic reaction.

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 of the cross-reacting proteins.

* 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

Misdiagnosis

As with many such reactions, systemic reactions to food are often self-diagnosed by patients as OAS when in fact it is not. Physicians attribute OAS only to reactions that are the result of an immunologic response, specifically, triggered by IgE antibodies.

Notes

Published studies

  • Konstantinou, G. N.; Grattan, C. E. H. (July 2008), "Food contact hypersensitivity syndrome: the mucosal contact urticaria paradigm". Clinical & Experimental Dermatology. 33 (4):383-389
  • Marcucci, F.; Frati, F.; Sensi, L.; Cara, G. D.; Novembre, E.; Bernardini, R.; Canonica, G. W.; Passalacqua, G. (April 2005), "Evaluation of food-pollen cross-reactivity by nose–mouth cross-challenge in pollinosis with oral allergy syndrome" . Allergy. 60 (4):501-505
  • Roehr, C.C.; Edenharter, G.; Reimann, S.; Ehlers, I.; Worm, M.; Zuberbier, T.; Niggemann, B. (October 2004), "Food allergy and non-allergic food hypersensitivity in children and adolescents" Clinical & Experimental Allergy. 34 (10):1534-1541

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