###Human: Why do I get allergy on having some kind of seafood? ###Assistant: Hello. Allergy reaction is due to a specific particular protein or substance. Each group has a different type of protein. It varies from each. There are several types of shellfish, each containing different proteins like crustaceans include crabs, lobster, crayfish, shrimp, and prawn. Mollusks include squid, snails, clams, oysters, and scallops. Some people are allergic to only one type of shellfish but can eat others. Other people with shellfish allergy must avoid all seafood. So one may need not get an allergy to all group and family.