How common are food allergies?
Although 25 percent of people think they're allergic to certain foods, studies show that about only 6 percent of children and 2 percent of adults have a food allergy.
What’s the difference between food allergy and food intolerance?
A true food allergy is a reaction triggered by the immune system (the part of your body that fights infection). Far more people simply have a food intolerance, which is unpleasant symptoms triggered by food (but does not involve the immune system).
For example, milk allergy is much more common in children than in adults. However, most children outgrow the allergy by 2 or 3 years of age. Symptoms of milk allergy include hives, vomiting and breathing problems after consuming a dairy product. Many adults may experience symptoms similar to milk allergy, as adults often have trouble digesting the sugar in milk. This is called "lactose intolerance," and it isn't an allergy because it doesn't involve the immune system. The symptoms of lactose intolerance are bloating, cramping, nausea, gas and diarrhea.
Manifestations of Food Allergy: Evaluation and Management by SH Sicherer, M.D. (American Family Physician January 15, 1999, http://www.aafp.org/afp/990115ap/415.html)