This hypersensitivity, to the proteins found in shellfish, scaly fish, or crustaceans, causes 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.
Seafood allergies are usually treated with an exclusion diet and vigilant avoidance of foods that may be contaminated with shellfish or fish ingredients and/or oils. The most severe seafood allergy can cause a reaction called anaphylaxis, which is an emergency, requiring immediate attention. It is treated with Epinephrine (US name) /Adrenaline (UK, Aus, S.Afr name), which can be administered with an EpiPen.