Iodine and Shellfish Allergy: A Myth that Lingers

Close to 3% of the U.S. population is allergic to shellfish, according to the Journal of American Medical Association. For those affected, even a small bite of shrimp, lobster, or crab, can result in reactions from itching and hives to anaphylaxis.(1)

The protein tropomyosin is considered to be the main allergen in shellfish allergy.(2) It’s a myth that people allergic to shellfish are allergic to iodine, according to the American Academy of Allergy, Asthma, and Immunology. The myth lingers and continues to have an impact on patients and their healthcare, as iodine is a component in intravenous dye which is widely used for radiological procedures.

A study published in the medical journal Allergy, Asthma Proceedings demonstrated that allergic patients themselves are not well informed. The study enrolled 60 subjects with a confirmed shellfish allergy. When asked the source of the shellfish allergy, 92% answered “iodine.”(3)

The College of Allergy, Asthma, And Immunology addresses the iodine myth on its website: “Years ago doctors believed that shellfish allergy stemmed from increased amounts of iodine present in the shellfish, so patients with a shellfish allergy were told to avoid iodine. If you are allergic to shellfish, specific proteins found in these foods are the allergens, not iodine. There is about a three percent chance that if you are allergic to shellfish you will have a reaction to contrast dyes, but this percentage is about the same in people with no known shellfish allergy.”(4)

(1) Gupta, R. M.D., M.P.H., Journal of the American Medical Association, Prevalence and Severity of Food Allergies,
(2) Faber, M.A. M.D., Pascal, M. M.D., et. al., Allergy, Shellfish Allergens: Tropomyosin and Beyond,
(3) Huang, S.W. M.D., Allergy, Asthma Proceedings, Seafood and Iodine: An Analysis of a Medical Myth,
(4) American College of Allergy, Asthma, and Immunology, Is Shellfish Allergy Related to Iodine?