At some point, just about everyone will experience an unpleasant reaction after consuming a food. However, only a small percentage of these reactions are true allergic responses, caused by the immune system overreacting to some component of the offensive food. The rest are either toxic reactions or are due to food intolerances, which can be caused by a variety of factors, such as the lack of an enzyme necessary to thoroughly digest the food. For those people who truly have Food Allergies, however, it's vital to accurately diagnose the allergy and identify the reaction-provoking food so that serious—or even life-threatening—allergic reactions can be prevented. Some of the most common foods that cause allergic reactions are milk, eggs, wheat, soy, peanuts, tree nuts, fish, and shellfish.
Typical allergic reactions to foods are characterized by:
- Symptoms that begin within minutes to hours of eating, touching, inhaling, or otherwise coming in contact with the offending food.
- Symptoms that involve the nose, eyes, throat, skin, lungs, digestive system, and, less frequently, the cardiovascular system. (Examples include itching of the skin, tingling or burning of the mouth and throat, sneezing, a runny nose, swelling of the eyelids, vomiting, abdominal pain, diarrhea, and difficulty breathing.) For more, see our section on symptoms.
- Reactions that may range in severity from annoying to life threatening.
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Food Allergies are caused by the same basic mechanism as other allergies; they result from an overreaction of the body's immune system to a normally harmless substance. Under usual circumstances, the body deploys the immune system to fight off foreign invaders like parasites, bacteria, or viruses. Allergic reactions occur when the immune system misidentifies harmless foreign substances and reacts to them as if they posed a threat. These substances are called allergens. The allergens that cause the majority of allergic reactions are plant pollens, mold spores, house dust mites, cockroaches, and animal dander (flakes of skin and other debris shed by an animal). Allergic reactions to foods, insect venom, medications, and latex occur less frequently but are not uncommon and tend to be more severe.
Irritants like tobacco smoke, perfumes, or strong cleaning products can make allergy symptoms worse and trigger asthma but are not allergens.
With the first exposures to an allergen, there are no symptoms, but in people who are genetically predisposed to become allergic, the immune system produces an antibody directed against the allergen called IgE. Once produced, IgE attaches to a receptor on the surface of a specialized cell in the body called a mast cell. The next time the body is exposed to the allergen, the IgE antibody tells these specialized cells to release chemicals, including histamine, which cause the symptoms of the allergic reaction.
Asthma and allergies have both been on the rise for several decades, especially in developed countries. One possible explanation for this, called the "hygiene hypothesis," proposes that children in these countries are exposed to fewer infectious organisms than in the past. As a result, their developing immune systems lack the degree of stimulation by certain bacteria and bacterial products needed for appropriate maturation—and they thus overreact to allergens.
If you have a parent or sibling who has an allergy, you are at higher risk of developing an allergy yourself. If the genes necessary for the development of allergies are inherited, the immune system becomes sensitized to a food or other allergen through initial exposures. Once allergic sensitization of the immune system has occurred, subsequent exposures to the allergen result in an allergic reaction.
Food Allergies are estimated to occur in 6 to 8 percent of infants and young children. A number of these children outgrow their Food Allergies with some outgrowing them in the first several years of life and others not doing so until adolescence. Compared with other conditions such as allergic nasal symptoms, the prevalence of food allergy in adults is relatively low: Approximately 3 to 4 percent of adults are thought to be affected.
Last reviewed on 11/6/09
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