Shellfish allergies are among the top 9 most common food allergies in the United States, affecting approximately 6.6 million Americans. However, it’s important to note that not all seafood allergies are the same. Two major groups of shellfish, mollusks and crustaceans, can trigger allergic reactions, but they differ in their allergenic proteins and how they each affect individuals. If you or someone you know has a shellfish allergy, understanding these differences is crucial.
What are mollusks and crustaceans
Both mollusks and crustaceans fall under the broad category of shellfish, but they belong to different biological groups:
- Mollusks: includes clams, oysters, mussels, scallops, squid (calamari), and octopuses. They are soft-bodied invertebrates, usually wholly or partly enclosed in a shell.
- Crustaceans: includes shrimp, prawns, crab, lobster, crayfish, and krill. They have segmented bodies, jointed limbs, and hard exoskeletons.
Why some people react to one but not the other
The main reason some individuals react to one group and not the other is due to differences in their allergenic proteins. For example, the primary allergen found in crustaceans is tropomyosin, a protein also found in insects and dust mites. Because of this, it’s common for people who have a crustacean allergy to also have a reaction to cockroaches or dust mites. With mollusk allergens, their version of the tropomyosin protein differs slightly from that found in crustaceans. This means some people allergic to crustaceans can tolerate mollusks, while others react to both.
Can you be allergic to both?
Yes, cross-reactivity (an allergic reaction that occurs when proteins in one substance are similar to the proteins in another) between mollusks and crustaceans is possible but doesn’t happen to everyone. Studies show that up to 75% of people with a crustacean allergy may also react to mollusks, but some individuals can eat mollusks safely despite a crustacean allergy. If you have a known allergy to one group, it’s best to consult an allergist before consuming the other.
Common symptoms of shellfish allergies
Allergic reactions to mollusks and crustaceans can range from mild to severe, including:
- Skin reactions: including hives, itching, and swelling
- Gastrointestinal issues: such as nausea, vomiting and diarrhea
- Respiratory symptoms: like wheezing, shortness of breath, and nasal congestion
- Anaphylaxis, a life-threatening reaction that requires immediate medical attention
Some precautionary measures you should take include checking food labels, avoiding cross-contact, and carrying an epinephrine auto-injector (EpiPen). These are important steps to take for any food allergy or sensitivity regardless of what it is.
Understanding the difference between mollusk and crustacean allergies can help you make safer choices when dining out. While some people react to both, others may tolerate mollusks even if they’re allergic to crustaceans. If you suspect a shellfish allergy, it’s important that you seek allergy testing and medical advice before consuming seafood.
