A true food allergy or food hypersensitivity is an adverse reaction to a food or food component that involves the body’s immune system. Using milk as an example, an immunologic response would be cow’s milk protein allergy, whereas the nonimmunologic response would be lactose intolerance, due to lactase deficiency. Although many people believe they have a food allergy, true food allergies are rare, affecting 1-3% of children under 6 years and less than 2% of adults in the general population.
While any food protein is potentially capable of eliciting an allergic reaction, most reactions are due to a limited number of foods. The ‘big five’ – egg, milk, peanut, soy and wheat – account for ~ 85% of food allergies. If you add fish and tree nuts to that list you have now identified the cause of 95% of reactions.
Responses to food allergies can be quite variable from individual to individual. It may involve gastrointestinal reactions including nausea, abdominal cramps, vomiting, and diarrhea, itchy rash, hives, asthma and hay fever, swelling of the lips, tongue and throat, migraine headaches and in severe cases, anaphylaxis. Some cases of food-induced hives or anaphylaxis are dependent on a cofactor for exacerbation of clinical symptoms. The only cofactor clearly demonstrated to provoke symptoms is exercise.
If there is a reasonable suspicion of food allergy, the first step is allergy skin testing to the suspected foods.