Food allergies are on the rise, though it isn?t clear why. According to the Centers for Disease Control and Prevention, more than one in 20 American children?particularly children born in the U.S.?cannot eat at least one usually perfectly innocuous food item because it causes a serious, possibly even fatal, allergic reaction, up from one in 30 about 15 years ago. Most of these children are allergic to one or more of the big eight?peanuts, tree nuts, milk, eggs, wheat, soy, fish, or shellfish collectively cause 90 percent of food reactions?but a broad range of foods can potentially cause a reaction. However, it?s rare for a person to be allergic to more than one food, except in cases where a small group or related foods all cause reactions.
Allergic reactions can be as minor as a little itching or as severe as anaphylaxis, in which swelling constricts the airway and also impedes blood circulation. People also vary in tolerance; some people can?t even be downwind of an allergen, particularly with peanut allergies. Sensitivity and severity generally sometimes increase over time, though not always, and it can be difficult to predict. In any event, it is not safe or healthy to deliberately expose someone to an allergen to build tolerance to it.
The mechanism of allergies is similar to autoimmune disease, an immune response to what should be a safe trigger?food in the case of allergies, rather than healthy body tissue. Researchers aren?t entirely sure why this happens, but one common speculation is what?s called the hygiene hypothesis. The immune system trains on common infectious agents in the natural environment. In an overly hygienic environment, however, these infectious agents are absent, causing the immune system to lock onto something like food or healthy organs or other tissue as a substitute. The result is allergy or autoimmune disease.
In some cases, allergies simply go away; children are more often allergic to foods than adults are, and some allergies are almost exclusively found in children. More commonly, a person has no choice but to to avoid things that cause allergic reactions. Experimental treatments do exist, including medications to block the action of the protein involved in the immune reactions involved in allergies.