A shellfish allergy occurs when a person’s immune system reacts to the proteins in a particular shellfish. This type of allergy is most often a severe allergy and can be life threatening. It is more common in adults, and is less likely to be outgrown. People who are allergic to one type of fish are likely to develop an allergy to other fish.

Shellfish allergy is an allergic reaction to a crustacean or mollusk.  The crustacean family includes shrimp, lobster, crab, prawn, crayfish.  The mollusks family includes mussels, clams, scallop, snails, octopus and squid (squid lost their shells throughout evolution and are still a threat to the shellfish allergic).

A fish allergy is often mistaken for an allergy to the parasite Anisakis.  Consider being tested for this parasite if you have a reaction to fish but your allergy test is negative. After cooking or freezing food this parasite is killed; however, it can still cause a serious allergic reaction.  Avoid all fish or shellfish if you are allergic to Anisakis.

It is possible to be allergic to one type of fish or shellfish and not to others; for example, you can be allergic to crustaceans such as shrimp and lobster, but not to mollusks such as oysters or clams.