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production and attachment to mast cell and basophil membranes is known as sensitization.
No symptoms occur during the sensitization process. However, upon a second exposure of the sensitized individual to the same allergen, the allergen cross-links IgE molecules on the surface of the mast cell or basophil membrane, stimulating the cells to degranulate and release the mediators mentioned above. These mediators circulate throughout the body and interact with receptors in various tissues, leading to the development of a wide range of possible symptoms. In IgE-mediated allergies, the interaction of very small amounts of the allergen with the membrane-bound IgE results in the release of massive quantities of histamine and the other mediators. Hence, consumers with IgE-mediated food allergies have a very low tolerance for the offending food.
Allergies to various environmental substances (pollens, mold spores, animal danders, dust mites, etc.), bee venom and certain drugs (e.g. penicillin) also occur through this same IgE-mediated mechanism. The only difference is the source, nature, route of exposure and identity of the allergen.
Individuals with IgE-mediated food allergies can tolerate very little of the offending food in their diet. Recent studies have shown that the tolerance dose for peanut among peanut-allergic individuals ranges from 2 mg to >50 mg for development of objective symptoms and down to as little as 100 |ig for development of mild subjective symptoms (9). The severity of the symptoms will vary with the amount consumed. While milligram levels of allergenic foods might not provoke reactions in all sensitive individuals, serious reactions have been provoked in some allergic individuals by ingestion of milligram levels of peanuts and tree nuts (10, 11). Some individuals are clearly more sensitive than others (9).
A variety of different symptoms can be involved with IgE-mediated food allergy (2). Different individuals will experience different symptoms on exposure to the same offending food. Gastrointestinal symptoms (nausea, vomiting and diarrhea) are very common because the gastrointestinal tract is the organ of initial insult in food allergies. Cutaneous symptoms (hives, itching, eczema and swelling) are also fairly common; eczema is especially common in infants. Respiratory symptoms (rhinitis, asthma) are uncommon symptoms with food allergies but asthma is a very serious, potentially life-threatening manifestation (12). Anaphylactic shock is the most frightening symptom associated with food allergies, although fortunately it is fairly rare. Anaphylactic shock involves multiple effects of the mediators on numerous tissues with gastrointestinal, cutaneous, respiratory and cardiovascular symptoms. Death can occur within 15 min of the onset of anaphylactic shock. Deaths have been documented from inadvertent consumption of the offending food by those with extraordinary degrees of allergic sensitivity (12, 13).
Allergies can develop at any age but they develop most commonly in infancy or early childhood (7). Most infants outgrow their food allergies within a matter of months or years (14). Some food allergies are much more commonly outgrown
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