The Shellfish Allergy Diet Guide

Crab is a crustacean shellfish. David Trood/Getty Images

Shellfish allergy is the most common food allergy among adults in the United States. About two percent of American adults have a shellfish allergy, and 0.1 percent of children have a shellfish allergy. Unlike many food allergies, shellfish allergy is more likely to develop in adulthood than in early childhood. In fact, around 60% of people with shellfish allergy experience their first reaction during adulthood. Shellfish allergies tend to be severe, lifelong food allergies.

Shellfish, Defined

Shellfish are divided into two types: mollusks and crustaceans. Mollusks include clams, oysters, mussels, and scallops. Crustaceans include shrimp, lobster, and crayfish. Shellfish may live in fresh or salt water - or even on land.

Shrimp, crab, and lobster cause most shellfish allergies.

Shellfish Allergy Symptoms

Allergic symptoms of shellfish allergy usually appear within minutes and up to two hours of eating shellfish. Symptoms may include:

  • Skin reactions such as hives or eczema.
  • Allergic conjunctivitis manifested by itchy, red, watery eyes.
  • Gastrointestinal reactions including nausea, abdominal pain, vomiting, or diarrhea, or a combination of these symptoms.
  • Airway symptoms including wheezing, coughing or a runny nose and/or a combination of these symptoms.
  • Angioedema including swelling of lips, tongue, or face.

Shellfish allergies may cause a severe reaction called anaphylaxis. Anaphylaxis is a serious medical emergency and requires immediate medical care. Many people with shellfish allergy carry a source of epinephrine, such as an Epi-Pen, in the event of a severe allergic reaction.

Shellfish allergy is the most common cause of exercise-induced anaphylaxis, where the consumption of a food allergen such as shellfish, coupled with exercise, may trigger an anaphylactic reaction.


People who are allergic to one type of crustacean, such as shrimp, are generally allergic to all other crustaceans. However, if you are allergic to crustaceans, you may not be allergic to mollusks. Allergy testing is the safest way to determine which shellfish, if any, you will be able to eat. Consult with your doctor before eating any new type of shellfish.

The allergenic protein in shellfish is called tropomyosin. Tropomyosin is also found in land snails, dust mites, cockroaches, and other insects. People with shellfish allergies may also experience symptoms to these substances and insects.


Shellfish allergy is usually diagnosed by a medical doctor (allergist) after medical history, physical examination, and food allergy testing are performed.


The treatment for shellfish allergy is the elimination of shellfish and foods made with shellfish from the diet.

If you have been diagnosed with a severe shellfish allergy, your doctor will prescribe an epinephrine auto-injector (commonly called an Epi-Pen) that you will need to carry with you at all times.

How to Avoid Shellfish

As one of the most common food allergens in the United States, crustacean shellfish is covered under the Food Allergy Labeling and Consumer Protection Act (FALCPA). As such, manufacturers must label the presence of crustacean shellfish in clear language on food labels, either in the list of ingredients or following the word "contains" after the ingredient list. Be sure you know how to read an ingredients list.

FALCPA does not include the labeling of mollusk shellfish. This means that manufacturers are not required to list the presence of clams, oysters, mussels, scallops or other mollusks in their ingredient lists. Those with mollusk shellfish allergy must be very careful with food products and err on the side of caution.

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 learn to ask questions when you eat in restaurants.

Foods to Avoid with a Shellfish Allergy

Some of the most common types of crustacean shellfish include:

  • Crab
  • Crawfish (Crayfish or Crawdads)
  • Langoustines (lobster)
  • Lobster
  • Prawns
  • Sea urchin
  • Shrimp

People who are allergic to mollusks should avoid all mollusks:

  • Abalone
  • Clam (Quahog)
  • Cockle
  • Limpet
  • Mussels
  • Octopus
  • Oysters
  • Scallops
  • Snails (Escargot - both sea and land snails should be avoided)
  • Squid (Calamari)
  • Surimi (imitation shellfish)
  • Whelk

Shellfish Allergy and Iodine

There are unsubstantiated concerns of cross-reactivity between shellfish allergy and iodine or radiocontrast allergy; some old medical forms still list this incorrectly as a contraindication. If you are allergic to shellfish, you do not need to avoid iodine or radiocontrast material. It is possible to be allergic to iodine or radiocontrast material, but those allergies are not related to shellfish allergies.

Shellfish Poisoning

The symptoms of shellfish poisoning (also called paralytic shellfish poisoning and red tide) usually occur within 30 minutes of eating tainted shellfish, and may be confused with an allergic reaction. Shellfish poisoning is caused by a very potent toxin called saxitoxin that is released by algae-like organisms that live in bivalve mollusks, such as clams and oysters. This kind of toxin only affects mollusks, and not fish or lobster. Symptoms of shellfish poisoning may include tingling or burning in the mouth or extremities, nausea, vomiting, and diarrhea. Shellfish poisoning can be very serious and even fatal. If you experience any of these symptoms after eating shellfish, seek emergency medical care.

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