The most common protein allergens in the United States, according to the AAAI, appear to be cow's milk, egg white, peanuts, wheat and soy, although shrimp, tomato, codfish and crab contain proteins to which some people are allergic, too. Cooking can reduce the effect of some protein allergens but may increase the effect of others. A food allergy may show up as hives, a skin reaction in which red, itchy, swollen areas suddenly appear, then soon disappear. Patients with suspected food allergies will be given a complete physical examination and asked by their doctor about the frequency, severity, seasonality and nature of their symptoms. Skin testing with a liquid extract of suspect foods may be used, but the technique is not as reliable as when testing for pollen allergies.
Blood tests are also useful for diagnosis for some patients in some instances.
One recognized food allergy is a reaction to sulfites. These are preservatives added to foods, usually during manufacturing but sometimes at the point of sale, as with some restaurant salad bars. Sulfites are harmless to most people but can cause reactions that are severe and sometimes fatal to those sensitive to them, especially to persons with asthma. FDA requires that products containing sulfites be labeled so that consumers who wish to can avoid them. Less than 1 percent of the population is thought to be sensitive to sulfites.