Food Allergy—It's Nothing to Sneeze At
The term food allergy is often misapplied, leading many people to believe that they are allergic to certain foods. A more accurate term would be food intolerance for many of these people. Food allergy symptoms can be caused either by a true allergic reaction to food or by simple food intolerance to specific components of a food. Symptoms may range from an upset stomach to life-threatening anaphylaxis. Identification and avoidance of any foods that trigger a reaction is the only cure available for food allergy.
What Is a Food Allergy?
A food allergy refers to a specific allergic reaction that involves the immune system, is triggered by a particular food, and is reproducible. In other words, the same symptoms—for example, wheezing or rash—must occur each time the food is eaten. It can also be called a hypersensitivity reaction as the immune system is very sensitive to the food.Food intolerance, on the other hand, is an adverse reaction to a food and does not involve the immune system. Food intolerance symptoms may be inconsistent. Reactions to the suspected food may vary in severity with each exposure, or may not occur at all.
What Causes a Food Hypersensitivity Reaction?
Food hypersensitivity is triggered by allergens—food components (usually proteins) that react with the immune system. Many different allergens can be present in the same food. Cow's milk, eggs, shellfish (shrimp, crab, or lobster), peanuts, tree nuts (walnuts, cashews, Brazil nuts), fish, soy, wheat, and even sesame seeds are the allergens that often trigger food hypersensitivity reactions.Food hypersensitivity, especially to cow's milk, is seen more often in children than in adults. Many children outgrow food hypersensitivities in later years, with sensitivity to milk, egg, and soy the most likely to wane over time. People who are sensitive to seafood or nuts, however, will probably have to avoid those foods forever.
Why Do Reactions Occur?
People who are allergic to certain foods are simply more sensitive to the allergens found in these foods. Allergic reactions to food result from the actions of a specific group of proteins called antibodies. Antibodies, an important part of the body's defense system, are activated when the offending food is eaten. Their role is to recognize foreign invaders (antigens)—in this case, allergens—and get rid of them. It is not known why the body will suddenly react to these food antigens as foreign invaders. Certain types of antibodies, known as IgE, are more highly reactive, and usually more abundant, in people with food hypersensitivity.When IgE antibodies encounter a food allergen to which they are sensitized, they attach themselves onto the food proteins. This attachment causes the immune system to release mediators—chemical messengers that travel through the bloodstream to alert other organs to the presence of an unwelcome protein guest.Release of these mediators causes the uncomfortable—or occasionally dangerous—symptoms of an allergic reaction. The extent of the reaction depends on the quantity of food eaten, age and health status, and the route taken by the mediators. The 3 most common reaction sites include:
Symptoms of allergic reaction in the skin include rash, hives
, and swelling of the skin and tissues of the face, lips, mouth, and throat, larynx, extremities, and genitalia. Itching and eczema
(an itchy, scaly skin rash) are also common but usually occur several hours to days after the offending food is ingested. Hives and swelling are usually immediate reactions, typically occurring within minutes (sometimes seconds) of food ingestion. They sometimes require immediate treatment.
Mediators that travel to the GI tract may cause symptoms along its entire length: swelling of the lips, itchy mouth or throat, nausea and vomiting, cramps and bloating, abdominal distention or intense abdominal pain, and diarrhea
Symptoms that affect breathing may include asthma
(stuffy, swollen, or runny nose), wheezing, or difficulty breathing.
Anaphylactic ShockAnaphylactic shock
is an extremely severe and life-threatening type of allergic reaction. The symptoms occur in rapid succession, progressing from itching or throat swelling to difficulty breathing, and loss of consciousness or even death, if emergency treatment is not started.