Shellfish allergies are a common food allergy that can trigger reactions ranging from mild discomfort to severe, life-threatening responses. They occur when the immune system mistakenly identifies harmless proteins in shellfish as threats. These allergies are among the most common food allergies in adults, often appearing first in adulthood.
Specific Allergies Within Shellfish
It is possible to be allergic to certain types of shellfish, such as crab, while tolerating others, like shrimp. While many individuals with a shellfish allergy react to multiple types within the same group (e.g., crustaceans like crab, shrimp, and lobster), this is not always the case. Some people can safely consume shrimp but experience adverse reactions to crab, or vice versa. This difference arises because even within the same category of shellfish, the specific allergenic proteins can vary subtly. Consulting an allergist for identification of triggering allergens is recommended.
Key Allergenic Proteins
The primary protein responsible for most shellfish allergies is tropomyosin, a muscle protein found across various invertebrate species. While tropomyosin is prevalent in crustaceans like shrimp, crab, and lobster, its molecular structure can differ slightly from one species to another. These structural variations mean that a person’s immune system might recognize and react to the tropomyosin in crab but not to the slightly different version found in shrimp. The amino acid sequences of tropomyosin can overlap significantly between species, yet sufficient differences can exist for specific sensitivities.
Beyond tropomyosin, other minor allergenic proteins can also contribute to shellfish allergies. These include arginine kinase, myosin light chain, and sarcoplasmic calcium-binding protein. The presence and characteristics of these additional proteins can further explain why an individual might react to one type of shellfish and not another. Sarcoplasmic calcium-binding protein, for instance, has been identified as a relevant allergen, particularly in children with shrimp allergy. This complexity highlights the individualized nature of shellfish allergies.
Managing Shellfish Allergies
Accurate diagnosis by an allergist is the first step in managing a shellfish allergy. Diagnosis involves skin prick tests, where small amounts of shellfish proteins are applied to the skin to observe a reaction, or blood tests, which measure allergen-specific IgE antibodies in the bloodstream. A healthcare professional interprets these results alongside a patient’s clinical history to confirm sensitivities. Sometimes, an oral food challenge under medical supervision may be performed if the diagnosis remains unclear.
Once diagnosed, strict avoidance of the identified allergens is the primary management strategy. This includes carefully reading food labels, as manufacturers in the United States must declare crustacean shellfish as a major allergen. Awareness of cross-contamination risks is also important, especially when dining out, as even trace amounts of shellfish protein can trigger a reaction. Individuals at risk of a severe reaction, such as anaphylaxis, should carry an epinephrine auto-injector and an emergency action plan. Epinephrine is the immediate treatment for anaphylaxis and should be administered at the first sign of a severe reaction.