What Is It?

A food allergy is a reaction by the body's immune system to a protein in a food. The food protein that causes an allergic reaction is called an allergen. When a person with a food allergy eats the food containing the allergen, a chain of chemical reactions can be triggered, causing inflammation and irritation in the skin, digestive and respiratory systems. Most allergic reactions occur within 30 minutes of consuming the problem food. Often, the reaction occurs within five to 10 minutes, but it can occur as long as four to six hours after ingestion. In extreme cases, the result can be anaphylaxis, a potentially life-threatening condition marked by faintness, rapid pulse, difficulty breathing and other severe symptoms requiring emergency medical treatment.

Many children who are thought to have a food allergy actually have food intolerance. Food intolerance involves a physical reaction to the food itself or to an additive in the food. Food intolerance does not involve the immune system. Lactose intolerance is the most common type of food intolerance. It occurs in people who do not have enough lactase, the enzyme needed to digest lactose, the sugar in milk. After eating or drinking dairy products, people with lactose intolerance can experience bloating, gas, abdominal pain or diarrhea. Food additives, including flavor enhancers, such as MSG, or preservatives, such as sulfites, also can trigger a food-intolerance reaction.

Food allergy is not as common as generally believed. Although many people think they have food allergies, only about 1% of adults do. Approximately 8% of preschool children and 2% of older children have food allergies. Controlled studies with newborns have found that about 2% of infants have either a milk allergy or milk intolerance. Children of parents who have a history of food allergies have the highest risk of developing food allergies.

Most food allergies are caused by a few foods. In young children, the foods most likely to cause allergies are cow's milk, eggs, wheat and peanuts. In older children and adults, peanut and seafood allergies are most common. Other foods that commonly cause allergic reactions include soy products and tree nuts, such as almonds, pecans and Brazil nuts.