The protein most often linked to shellfish allergy, called “tropomyosin,” is found in all types of shellfish, including abalone, clams, cockle, crab, crayfish, lobster, mollusks, mussels, octopus, oysters, scallops, shrimp, snails, and squid. The likelihood that a person who is allergic to one type of shellfish, such as shrimp, is allergic to another, such as lobster, is approximately 75%. Although people of any age can develop a shellfish allergy, it occurs most commonly in adults.
Shellfish allergy is also more common in women. After taking a careful history, allergy testing to shellfish by skin testing or blood testing is the most reliable way to tell if the person is truly allergic. Adverse reactions to shellfish are also sometimes caused by a nonallergic reaction, such as food poisoning.