People with allergies must avoid the offending foods altogether. Cow's milk, eggs, wheat, and soy are the most common sources of food allergies in children. Allergists believe that infant allergies are the result of immunologic immaturity and, to some extent, intestinal immaturity. Children sometimes outgrow the allergies they had as infants, but an early peanut allergy may be lifelong. Adults are usually most affected by tree nuts, fish, shellfish, and peanuts.
Food intolerance is a much more common problem than allergy.
Here, the problem is not with the body's immune system, but, rather, with its metabolism. The body cannot adequately digest a portion of the offending food, usually because of some chemical deficiency. The deficiency can cause cramps and diarrhea if milk is consumed. Estimates are that about 80 percent of African-Americans have lactose intolerance, as do many people of Mediterranean or Hispanic origin. It is quite different from the true allergic reaction some have to the proteins in milk.