Shellfish is one of the more common food allergies. This allergy usually is lifelong. About 60 percent of people with shellfish allergy experience their first allergic reaction as adults.
There are two groups of shellfish: crustacea (such as shrimp, crab and lobster) and mollusks (such as clams, mussels, oysters and scallops). Crustacea cause most shellfish reactions, and these tend to be severe.
Finned fish and shellfish are not related. Being allergic to one does not always mean that you must avoid both.
Shellfish can cause severe and potentially life-threatening allergic reactions (such as anaphylaxis). Allergic reactions can be unpredictable, and even very small amounts of shellfish can cause one.
If you have a shellfish allergy, keep an epinephrine auto-injector (such as an EpiPen®, Auvi-Q™ or Adrenaclick®) with you at all times. Epinephrine is the first-line treatment for anaphylaxis.
To prevent a reaction, it is very important to avoid all shellfish and shellfish products. Always read food labels and ask questions about ingredients before eating a food that you have not prepared yourself.
Most people who are allergic to one group of shellfish are allergic to other types. Your allergist will usually recommend you avoid all kinds of shellfish. If you are allergic to a specific type of shellfish but want to eat other shellfish, talk to your doctor about further allergy testing.
Steer clear of seafood restaurants, where there is a high risk of food cross-contact. You should also avoid touching shellfish and going to fish markets. Being in any area where shellfish are being cooked can put you at risk, as shellfish protein could be in the steam.
Shellfish is one of the eight major allergens that must be listed on packaged foods sold in the U.S., as required by federal law. Download this resource about how to identify shellfish on food labels.
Avoid foods that contain shellfish or any of these ingredients:
- Crawfish (crawdad, crayfish, ecrevisse)
- Lobster (langouste, langoustine, Moreton bay bugs, scampi, tomalley)
- Shrimp (crevette, scampi)
Your doctor may advise you to avoid mollusks* or these ingredients:
- Clams (cherrystone, geoduck, littleneck, pismo, quahog)
- Limpet (lapas, opihi)
- Sea cucumber
- Sea urchin
- Snails (escargot)
- Squid (calamari)
- Whelk (Turban shell)
*Note: The federal government does not require mollusks to be fully disclosed on product labels.
Shellfish are sometimes found in the following:
- Cuttlefish ink
- Fish stock
- Seafood flavoring (e.g., crab or clam extract)
Carrageenan, or "Irish moss,” is not shellfish. It is a red marine algae used as an emulsifier, stabilizer and thickener in many foods like dairy foods. It is safe for most people with food allergies.
Shellfish allergy is sometimes confused with iodine allergy because shellfish is known to contain the element iodine. But iodine is not what triggers the reaction in people who are allergic to shellfish. If you have a shellfish allergy, you do not need to worry about cross-reactions with iodine or radiocontrast material (which can contain iodine and is used in some radiographic medical procedures).
1Sicherer SH, Munoz-Furlong A, Sampson HA. Prevalence of seafood allergy in the United States determined by a random telephone survey. J Allergy Clin Immunol 2004; 114(1):159-65.
What to Read Next
Learn how to prevent cross-contact, which happens when an allergen is accidentally transferred from one food to another.
Managing life with a food allergy means reading packaged food labels—every time you purchase that food.