Allergies to Food
A food allergy is a reaction of the immune system to a food or food ingredient that most people find harmless. If you eat a food that produces an allergic reaction, your immune system responds by releasing numerous chemicals that cause allergic symptoms. A food allergy is different from a food intolerance, which does not trigger an immune response. A food intolerance (such as lactose intolerance) usually arises from an enzyme deficiency and produces symptoms such as stomach cramps, gas, or diarrhea. Food intolerances are relatively common, but a true food allergy is rare, affecting only about 1 percent of the population.
The most common foods that cause allergies in adults are fish and shellfish, eggs, and nuts—such as peanuts, walnuts, and pecans. Symptoms of food allergy can include skin reactions such as hives or rashes, nasal congestion, asthma attacks in people who have asthma, and gastrointestinal problems such as nausea, gas, or diarrhea. Because both food allergies and food intolerances can cause intestinal symptoms, the two disorders are easily confused and must be diagnosed by a doctor.
Food allergy symptoms can appear immediately after eating or may develop over time—within hours or even days. In severe cases the food can provoke a serious reaction known as anaphylaxis (see “Anaphylactic Shock,” Post), which can be life-threatening. Signs and symptoms of anaphylaxis include hives, difficulty breathing, a drop in blood pressure, and loss of consciousness.
To determine whether you have a true food allergy, your doctor probably will perform one of two tests: a skin prick test or a blood test called the radioallergosorbent test (RAST). During the skin prick test, the doctor deposits a small amount of the suspected food allergen onto your forearm and then pricks the skin beneath it with a needle. A small red bump will appear at the site if you are allergic to that particular food. For the RAST, a sample of your blood is taken and sent to a laboratory for analysis to determine whether your body has formed antibodies to the food in question. Your doctor also may ask you to record everything you eat in a food diary for a couple of weeks to help in the diagnosis.
Many people will outgrow food allergies, except allergies to nuts, fish, and shellfish. The best treatment for a food allergy is to avoid eating the food that causes the allergic reaction. You will need to read food labels carefully and ask questions when dining out to make sure that the foods you eat do not contain the allergen. Severe allergic reactions are life-threatening. If you have had a previous severe allergic reaction, you will need to carry an injecting device that contains epinephrine with you at all times, so you can inject yourself immediately if you have another allergic reaction.
Posted in Immune System
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