Normally, the immune response defends against potentially harmful substances such as bacteria, viruses, and toxins . The cause of food allergies is not fully understood, because they can produce such a variety of symptoms. The incidence is difficult to assess, because reporting is sporadic. Reactions to foods may vary from mild to fatal depending on the type and the severity of the reaction.
Food allergy is common.
The immune system releases antibodies and substances including histamine in response to ingestion of a particular food or food component. The symptoms may be localized to the stomach and intestines, or may involve many parts of the body after the food is digested or absorbed. The symptoms usually begin immediately, seldom more than 2 hours after eating. A food allergy is distinguished from food intolerance and other disorders by the production of antibodies and the release of histamine and similar substances. Asthma , eczema , or other disorders may be triggered or worsened by food allergies.