All food allergies are caused by an immune system problem. Your immune system identifies certain shellfish proteins as harmful, triggering the production of antibodies to the shellfish protein (allergen). The next time you come in contact with proteins in shellfish, these antibodies recognize them and signal your immune system to release histamine and other chemicals that cause allergy symptoms.

Histamine and other body chemicals cause a range of allergic signs and symptoms. Histamine is partly responsible for most allergic responses, including runny nose, itchy eyes, dry throat, rashes and hives, nausea, diarrhea, difficulty breathing, and in some cases, anaphylactic shock.

There are several types of shellfish, and each kind contains different allergy-causing proteins.

Crustaceans include crabs, lobster, crayfish, shrimp and prawn.

Mollusks include:

  • Bivalves, such as clams, mussels, oysters and scallops
  • Gastropods, such as limpets, periwinkles, snails (escargot) and abalone
  • Cephalopods, such as squid, cuttlefish and octopus

Some people are allergic to only one type of shellfish, but can eat others. However, some people with a shellfish allergy must avoid all shellfish.

Jun. 23, 2011