Shellfish Allergy: What You Need to Know

By Jeanette Bradley

Shellfish Allergy Overview:

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. Shellfish allergies tend to be severe, lifelong food allergies.

Symptoms of Shellfish Allergy:

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

• Skin reactions such as hives or eczema.
• Allergic conjunctivitis: Itchy, red, watery eyes.
• GI reactions such as nausea, abdominal pain, vomiting, or diarrhea.
• Airways symptoms such as wheezing or coughing or runny nose.
• Angioedema: Swelling of lips, tongue, or face

Shellfish allergies may cause a severe reaction called anaphylaxis. Anaphylaxis is a medical emergency that requires immediate medical care.
Shellfish allergy is the most common cause of Exercise-Induced Anaphylaxis, in which the combination of eating a food allergen and exercising causes anaphylaxis.

What Are Shellfish, Anyway?:

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.
People who are allergic to one type of crustacean, such as shrimp, are generally allergic to all other crustaceans. 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 land snails, dust mites, cockroaches, or other insects.

Living With a Shellfish Allergy:

Since there is no cure for shellfish allergy at this time, managing your shellfish allergy involves avoiding all shellfish and being prepared for future reactions. 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.
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.

Shellfish and Labeling Laws:

The Food Allergy Labeling Law (FALCPA) defines crustacean shellfish as one of the big eight allergens, but not mollusks. This means that 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, there is a likelihood that you may have a sensitivity to mollusks as well. Allergy testing can help you determine if mollusks are safe for you to eat.
You should always read ingredient labels carefully if you have shellfish allergies.

Shellfish Allergy and Iodine:

There are unsubstantiated concerns of a cross reactivity between shellfish allergy and iodine/contrast 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, so you do not need to worry about cross-reactions.

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 two-shelled mollusks, such as clams and oysters. As such, this kind of toxin only affects mollusks, and not fish or lobster. Symptoms may include tingling or burning in the mouth or extremities, nausea, vomiting, and diarrhea. Shellfish poisoning can be very serious or even fatal. If you experience any of these symptoms after eating shellfish, seek emergency medical care.

<sub>Sources:
FAAN. Shellfish Allergy. http://www.foodallergy.org/page/shellfish-allergy Accessed 2/10/2011.
NIAID-Sponsored Expert Panel. Guidelines for the Diagnosis and Management of Food Allergy in the United States: Report of the NIAID-Sponsored Expert Panel. The Journal of Allergy and Clinical Immunology. Volume 126, Issue 6, Supplement , Pages S1-S58, December 2010
Sheerin, Kathleen A. "Seafood Allergy."Allergy and Asthma Advocate. Winter 2006. 9 June 2007. 


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