This group includes crustaceans such as crabs, shrimp and lobsters, and molluscs such as oysters and snails.
Shellfish allergies are most commonly seen in adults, particularly those living in regions where they are often eaten. Researchers have estimated that 75% of individuals who are allergic to one type of crustacean (shrimp, lobster, crawfish or crab) are also allergic to other types. As crustaceans and molluscs (oysters, squid, scallops) contain the same type of proteins some people may react to both groups of foods.
Symptoms range from itching and swelling of the mouth and throat (oral allergy syndrome) to life threatening reactions.
Symptoms most often occur when the seafood is ingested, but can also occur when raw seafood is handled and even after inhaling steam while crustaceans such as shrimp is being cooked.
Cooking does not appear to destroy the allergens in crustaceans and molluscs. Shellfish allergens are usually found in the flesh and are part of the muscle protein system, whilst in foods such as shrimps, allergens have also been found in the shells.