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Food Allergies

Food Allergy

A food allergy is an allergic reaction to a particular food.
Many different foods can cause allergic reactions. However, food allergies are most commonly triggered by certain nuts, peanuts, shellfish, fish, milk, eggs, wheat, and soybeans. Allergic reactions to foods may be severe and sometimes include an anaphylactic reaction.

Food allergies may start during infancy. They are most common among children whose parents have food allergies, allergic rhinitis, or allergic asthma. Children with food allergies tend to be allergic to the most common allergens, such as those in eggs, milk, peanuts, and soybeans.
Food allergies are sometimes blamed for such disorders as hyperactivity in children, chronic fatigue, arthritis, poor athletic performance, and depression. However, these associations have not been substantiated.

Some reactions to food are not an allergic reaction. For example, food intolerance differs from a food allergy because it does not involve the immune system. Instead it involves a reaction in the digestive tract that results in digestive upset. For example, some people lack an enzyme necessary for digesting the sugar in milk (lactose). Other reactions to a food may result from contamination or deterioration of the food.

In some people, food additives can cause a reaction that resembles but is not an allergic reaction. For example, monosodium glutamate (MSG), some preservatives (such as metabisulfite), and dyes (such as tartrazine, a yellow dye used in candies, soft drinks, and other foods) can cause symptoms such as asthma and hives. Similarly, eating certain foods, such as cheese, wine, and chocolate, triggers migraine headaches in some people.

Symptoms

In infants, the first symptom of a food allergy may be a rash such as eczema (atopic dermatitis) or a rash that resembles hives. The rash may be accompanied by nausea, vomiting, and diarrhea. By about age 1 year, the rash often lessens. By about age 10, food allergies—most commonly to milk and less commonly to eggs and peanuts—tend to subside. Allergies to airborne substances, such as allergic asthma and hay fever, may develop as food allergies subside.

In adults, food allergies cause itching of the mouth, hives, eczema, and, occasionally, a runny nose and asthma. For some adults with a food allergy, eating a tiny amount of the food may trigger a severe reaction. A rash may cover the entire body, the throat may swell, and the airways may narrow, making breathing difficult. Occasionally, this reaction is a life-threatening anaphylactic reaction. For some people, allergic reactions to food occur only if they exercise immediately after eating the food.

Diagnosis

Doctors suspect a food allergy primarily on the basis of the person's history. Then skin tests with extracts from various foods may be performed. A reaction to a food tested does not necessarily mean that a person is allergic to that food, but no skin reaction means that an allergy to that food is unlikely. If the person reacts to the food tested, an oral challenge test may be performed to confirm the diagnosis. In this test, the suspected food is given in a carrier food such as milk or applesauce, and the doctor observes as the person eats the food. If no symptoms develop, the person is not allergic to the food.
Another way to identify the food allergy is an elimination diet. The person stops eating all foods that may be causing the symptoms for about 1 week.

The doctor provides the diet the person is to follow. Only the foods or fluids specified in the diet may be eaten, and only pure products should be used. Following such a diet is not easy, because many food products have ingredients that are not obvious or expected. For example, many rye breads contain some wheat flour. Eating in restaurants is not advisable, because the person and the doctor need to know the ingredients of every meal eaten. If no symptoms occur, foods are added back one at a time. Each added food is given for several days or until symptoms appear, and thus the allergen is identified.

Treatment

People with food allergies must eliminate the foods that trigger their allergies from their diet. Desensitization by first eliminating the food, then eating small amounts of the food or placing drops of food extracts under the tongue is not effective. Antihistamines are useful only for relieving hives and swelling. People with severe food allergies often carry antihistamines to take immediately if a reaction starts. They should also carry a self-injecting syringe of epinephrine to use when needed for severe reactions.



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