RecruitingNatural History and Genetics of Food Allergy and Related ConditionsBackground: \- About 15 million Americans have a food allergy. Because there are no cures or effective prevention or treatment for food allergies, researchers want to learn more about them. Objective: \- To learn more about the causes and effects of food allergy and related conditions. Eligibility: * People ages 2 99 who have food allergy and/or a related genetic or other condition * Their relatives * Healthy relatives and volunteers Design: * Participants will have at least 3 visits over 1 2 years, and then once a year for up to 12 years. Each may last a day or longer. * Participants will be screened with medical history, physical exam, and questionnaires. * Participants may have the following: * Blood tests * Allergy skin prick tests: Drops of allergens are placed on the back or arm. The skin is scratched under each drop. * Leukapheresis: blood is taken from a needle in one arm, passed through a machine, and returned through a needle in the other arm. * X-rays * Esophageal string test: One end of a string is taped to the cheek and the other end is packed into a capsule. When the capsule is swallowed, the string unwinds; it is left in for at least 1 hour. * EGD and colonoscopy: Biopsies are taken from the gastrointestinal system. * Tiny biopsies of skin * Photographs of the body * Collection of cells through: * Swab of nose, inside of cheek, or skin * Gentle skin scrape * Tape stripping: piece of tape is put on the skin and pulled off.