Seafood can be classified into three major groups -- fish, crustaceans and mollusks. For the purpose of seafood consumption, shellfish refers to both crustaceans and mollusks. Crustaceans include crabs, lobsters, prawns, and shrimps, and are actually related to mites and insects. Mollusks include mussels, oysters, abalone and squid. Fish are not related to shellfish, and belong to a different category of animals.
Allergy to ShellfishShellfish are a common cause of food allergy, particularly for adults, affecting approximately 2% of the population in the United States. In addition to allergic reactions, consumption of shellfish can lead to infections caused by bacteria, viruses, and parasites, as well as toxins and other chemicals found in shellfish. Additives like preservatives (such as sulfites), flavorings (such as MSG), spices, and hidden allergen ingredients (including the milk protein casein) may be responsible for allergic reactions and food intolerances experienced as a result of eating shellfish.
Causes of Shellfish AllergyThe major allergen responsible for allergic reactions caused by shellfish is called tropomyosin. Tropomyosin causes the majority of allergic reactions from crustaceans, although other allergens are important causes of allergic reactions from mollusks. Tropomyosins show high rates of cross-reactivity among shellfish -- therefore, a person with an allergy to one type of shellfish is very likely to be allergic to other shellfish, and therefore should avoid all shellfish. Since fish are not related to shellfish, and have different, unrelated allergens, a person with shellfish allergy should be able to consume fish.
Shellfish Allergy and Dust Mite AllergyDust mites and cockroaches are closely related to shellfish, and also have tropomyosins as a major allergen. People who are allergic to dust mites and cockroaches may become allergic to shellfish as well. There are reports of vegetarians who have never eaten shellfish, yet show sensitization to shellfish, probably as a result of allergy to dust mites. It is important to know that most people with dust mite allergy are not allergic to shellfish, but being allergic to one of these arthropods places a person at risk for allergy to the other.
Symptoms, Diagnosis and Treatment of Shellfish AllergyThe symptoms of shellfish allergy are similar to those of other food allergies, which can include anaphylaxis. People may also experience symptoms of oral allergy syndrome to shellfish, and cases of exercise-induced anaphylaxis have been reported after eating shellfish. Respiratory allergy symptoms, including allergic rhinitis and asthma, are common among shellfish-processing workers and restaurant workers who are allergic to shellfish. In fact, approximately 25% of people working in shellfish processing plants show sensitization to shellfish.
The diagnosis of shellfish allergy is based on a person’s symptoms as well as the presence of allergic antibody (IgE) against shellfish found on allergy testing. Skin testing is the most accurate test for diagnosing food allergy, although blood testing for shellfish allergy can also be helpful.
The treatment of shellfish allergy mostly involves the avoidance of all shellfish, given the high rates of cross-reactivity among these creatures. Symptoms of shellfish allergy are treated in much the same way as the treatment for other food allergies, including the use of injectable epinephrine and antihistamines. It is possible that the use of immunotherapy to dust mites and/or cockroaches could be curative for shellfish allergy in a person with allergies to all of these arthropods. Further studies in this area are needed before this can be routinely recommended, however.
You’ve just learned about shellfish allergy -- now find out about fish allergy.
Lopata AL, O’Hehir RE, Lehrer SB. Shellfish Allergy. Clinical and Experimental Allergy. 2010;(40):850-858.
DISCLAIMER: The information contained in this site is for educational purposes only, and should not be used as a substitute for personal care by a licensed physician. Please see your physician for diagnosis and treatment of any concerning symptoms or medical condition.