ADVICE: Why do I suddenly have an allergy to shellfish?

People with a history of other allergies are most likely to develop new ones.

Maja Begovic 3 minute read November 6, 2020
Shellfish allergy

Some people develop allergies to shellfish as adults. Getty

Dear Asking For a Friend,

I have spent my life eating shellfish, and now I’m allergic. How is this possible?

Signed, Hives

Dear Hives,

You’re not alone. More than 600,000 Canadians live with a shellfish allergy, according to AllerGen, a national research group for allergic disease, asthma and anaphylaxis. Shellfish is one of the leading causes of food allergy in adults and can cause anaphylaxis — a severe and life-threatening allergic reaction. Tropomyosin, a protein found in shellfish, is what sets off the reaction, and while it’s not clear why this happens, experts suggest that our immune system, along with a number of other factors are to blame.

What happens to your body?

“Almost everyone’s immune system correctly ignores all foods, so they can eat a food as much or as little as they want without ever having a problem,” says Dr. Timothy Vander Leek, Associate Clinical Professor for the Division of Clinical Immunology and Allergy, in the Department of Pediatrics at the University of Alberta, and President of the Canadian Society of Allergy and Clinical Immunology (CSACI). “For a very small number of people, their immune system stops ignoring the food and creates an allergic antibody to that food. We don’t understand why this happens, but it is more likely to happen to people with a history of other allergic problems, most importantly allergies to another food or if they have eczema.”

A shellfish allergy can cause symptoms such as hives, itchiness, abdominal pain, vomiting, and tingling in the mouth. It can also cause more severe and life-threatening reactions, such as a swollen throat, rapid pulse, breathing difficulties, and a loss of consciousness. As with most food allergies, symptoms can be unpredictable, and may develop within minutes or long after eating. It’s also possible to experience a more severe allergic reaction after each exposure to the food. According to Vander Leek, many people avoid shellfish and believe they are allergic because of an adverse reaction they may have experienced in the past. Allergy testing — in the form of a skin prick test — is the best way to determine whether you have an allergy or a food intolerance.

Can you prevent a food allergy?

The short answer is no. Vander Leek explains that for most people, eating shellfish or other common food allergens will often never cause any problems, but for others, an allergy may develop if a food is not eaten regularly. He says that it’s possible to have an allergic reaction to a food that you have not eaten in as little as four weeks.

The bottom line is that food allergies can happen to anyone, at any age, regardless of exposure. Some kids can outgrow a food allergy, but that’s not likely to happen with adults. If what you have is an allergy, you may need an EpiPen, which, in the event of a severe and life-threatening reaction, can save your life. The best way to stay safe is to avoid the food altogether and follow the advice of your health care provider.

Maja Begovic is a freelance writer with


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