Seafood allergy is a type of food allergy. It is a hypersensitivity to dietary substances from shellfish, scaly fish, or crustaceans, causing an overreaction of the immune system, which, for millions of people, may lead to severe physical symptoms, including anaphylaxis. The Asthma and Allergy Foundation of America estimates that the majority of pediatric and adult food allergy patients have a seafood allergy. It occurs mainly (but not exclusively) in adults.
Allergic reactions may result when the susceptible person is not consuming the allergenic substance, by exposure to vapours resulting from cooking of seafood or even preparation or handling.