The Symptoms and Management of Shellfish Allergies

Shellfish allergy is the most common food allergy among adults in the United States.

Unlike many food allergies, shellfish allergy is more likely to develop in adulthood than in early childhood. The majority of people who have shellfish allergies have their first reaction as adults. Once you develop a shellfish allergy, it tends to be severe and lifelong.

hand shucking oysters mollusk shellfish over ice
Greg Kessler / Getty Images


Symptoms of shellfish allergy usually appear within minutes up to two hours of eating shellfish.

These symptoms may include:

  • Skin reactions such as hives or eczema
  • Allergic conjunctivitis: Itchy, red, watery eyes
  • Digestive reactions such as nausea, abdominal pain, vomiting, or diarrhea
  • Airway symptoms such as wheezing or coughing or a runny nose
  • Angioedema: swelling of lips, tongue, throat, or face

Shellfish allergies may cause a severe reaction called anaphylaxis. Anaphylaxis is a life-threatening allergic reaction and a medical emergency that requires immediate medical care.

Shellfish allergy also is the most common cause of exercise-induced anaphylaxis, in which the combination of eating a food allergen and exercising causes an anaphylactic reaction.

What Are Shellfish?

Shellfish are divided into two families: mollusks and crustaceans.

  • Mollusks include clams, oysters, and squid.
  • Crustaceans include shrimp, lobster, and crayfish.

Shellfish may live in fresh or salt water, or even on land — land snails, for example, are shellfish.

People who are allergic to one type of crustacean, such as shrimp, are generally allergic to all other crustaceans as well. If you are allergic to crustaceans, you may or may not be able to eat mollusks, such as clams or oysters. Allergy testing is the safest way to determine which shellfish, if any, you will be able to eat.

The allergenic protein in shellfish (tropomyosin) is not only found in sea creatures. People with shellfish allergies may also have reactions to dust mites, cockroaches, or other insects.

Living With a Shellfish Allergy

Since there is no cure for shellfish allergy, managing your condition involves avoiding all shellfish and being prepared for future reactions. If you have been diagnosed with a severe shellfish allergy, your healthcare provider will prescribe an epinephrine auto-injector (commonly called an Epi-Pen) that you will need to carry with you at all times.

Avoiding shellfish may seem easy, but food allergens can lurk in surprising places. You will need to learn to read labels to avoid shellfish and to be very careful when you eat in restaurants.

The U.S. Food Allergy Labeling Law (FALCPA) includes crustacean shellfish as one of the big eight allergens that must be called out on food labels. However, mollusks aren't included, which means manufacturers are not required to list the presence of clams, oysters, mussels, scallops, or other mollusks in ingredient lists.

If you are allergic to crustacean shellfish, you're likely to also have a sensitivity to mollusks. Allergy testing can help you determine if mollusks are safe for you to eat, or if you have to avoid them.

Is Iodine a Problem?

Years ago, healthcare providers believed there was a possibility that people who were allergic to shellfish might also react to iodine, including iodine used in medical imaging. In fact, some old medical forms still list this as an issue.

But it's not true—we now know that if you're allergic to shellfish, you do not need to avoid iodine.

That being said, it's possible to be allergic to iodine itself, or to the formulations of iodine used in medical imaging. But if you do have that allergy, it's not related to a shellfish allergy, so you don't need to worry about cross-reactions.

Shellfish Poisoning Is Not an Allergy

Allergies aren't the only medical conditions related to shellfish. Shellfish poisoning (also called paralytic shellfish poisoning and red tide) is a condition caused by a very potent toxin called saxitoxin that is released by algae-like organisms that live in two-shelled mollusks, such as clams and oysters.

Symptoms may include tingling or burning in the mouth or extremities, nausea, vomiting, and diarrhea, and usually, occur within 30 minutes of eating tainted shellfish. These symptoms can be mistaken for an allergic reaction.

Shellfish poisoning can be very serious or even fatal. If you experience any of these symptoms after eating shellfish, seek emergency medical care.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Food Allergy Research & Education. Shellfish Allergy.

  2. Khora SS. Seafood-Associated Shellfish Allergy: A Comprehensive Review. Immunol Invest. 2016;45(6):504-30. doi: 10.1080/08820139.2016.1180301

  3. Food and Drug Administration. What You Need to Know about Food Allergies.

By Jeanette Bradley
Jeanette Bradley is a noted food allergy advocate and author of the cookbook, "Food Allergy Kitchen Wizardry: 125 Recipes for People with Allergies"