The following are possible factors that contribute to immunological sensitization leading to food intolerance:
1. Genetic predisposition: food allergy is commonly familial, suggesting the importance of genetic factors.
2. Immaturity of the immune system or the gastrointestinal mucosal barrier in newborn infants may predispose to sensitisation. The numerous studies that have been performed to determine if food allergy or atopic disease can be prevented by interventions during pregnancy or lactation are based on the idea that there is a critical period during which sensitization can occur.
3. Dosage of antigen: It may be that high dosage leads to the development of tolerance, and low dosage leads to sensitization. This might help to explain the well-documented phenomenon of infants who become allergic to traces of foods that reach them through their mother's breast milk.
4. Certain food antigens are especially likely to lead to sensitization, such as egg, cow's milk, and peanut. The reason why certain foods are more likely to provoke an allergic reaction than others is poorly understood.
5. A triggering event, such as a viral infection: The evidence is anecdotal, but there is a suggestion that food allergy may develop in a previously nonallergic subject after a viral infection such as infectious mononucleosis (glandular fever).
6. Alteration in the permeability of the gastrointestinal tract, permitting abnormal antigen access: The best example of this is the suggestion that acute viral gastroenteritis may damage the small intestinal mucosa, allowing abnormal absorption of food proteins, leading to sensitization. Thus, some data suggest that in a few cases the onset of cow's milk protein allergy follows soon after an episode of gastroenteritis.
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