Have you ever heard the saying “A fish is a fish is a fish?” When it comes to food allergies, that’s not necessarily the case. Although some people can be highly allergic to one type of seafood, they may be able to eat other types. For instance, some individuals find that they can eat shrimp as often as they want, but they get very sick if they eat crabs.

“I stay away from anything with crab — it’s my only seafood allergy,” one MyFoodAllergyTeam member wrote.

If you’re allergic to crab, keep reading to learn what this could mean about eating shrimp and other types of fish.

Is Crab a Shellfish?

Crabs are a type of shellfish and are considered crustaceans. Other crustaceans include shrimp, lobster, crayfish, and prawns. Mollusks, another type of shellfish, include scallops, mussels, snails, octopus, squid, clams, and abalone.

Most people who are allergic to one class of shellfish (for instance, crustaceans) also experience allergic reactions from other foods in that class. But not everyone is in that category. It’s possible to be allergic to specific species of shellfish, such as certain types of crabs, without being allergic to shrimp.

In addition, people allergic to shellfish won’t necessarily be allergic to finned fish (like salmon or flounder). Shellfish and finned fish are very different from one another. “I can eat fish, but if I eat crab, my entire face swells up,” one MyFoodAllergyTeam member wrote.

How Common Are Shellfish Allergies?

About 2 percent of people in the United States have a shellfish allergy. It’s the most common allergy among adults and also occurs often in children.

According to Cleveland Clinic, about 60 percent of people with shellfish allergies get their first symptoms as adults. Some health experts believe this may be because children don’t often eat shellfish. Shrimp, crabs, and lobster cause the most allergic reactions among all shellfish.

Shellfish Allergy Symptoms

Reactions to shellfish may vary, causing mild allergy symptoms in some people and severe symptoms in others. Mild symptoms may include:

• Swollen eyes, lips, and face
• Welts or hives on your skin
• Vomiting or abdominal pain

Severe shellfish allergy symptoms may cause a serious reaction called anaphylaxis. Anaphylaxis can be life-threatening, causing your throat to close up and affecting your ability to breathe. Anaphylaxis symptoms that indicate a severe allergic reaction may include:

• Throat tightness or swelling
• Trouble breathing or shortness of breath
• A cough or wheezing
• A swollen tongue
• Dizziness
• Difficulty talking
• A hoarse voice

If you experience anaphylaxis, it’s important to use your emergency food allergy medications, such as an epinephrine auto-injector, right away. You should also call 911 for medical care.

Treating Shellfish Allergies

The best way to treat an allergy to shrimp, crab, or other shellfish is to avoid exposure to the allergen. Shellfish are among the nine major allergens recognized under U.S. law, so packaged food manufacturers are required to list these ingredients on labels. Check the labels of every food you’re buying, and always tell restaurant staff about your allergies so they can confirm with the chef that your dish is safe to eat.

Although crab ingredients aren’t often hidden in other products, it’s still important to check every label. For instance, some foods (such as some varieties of kimchi, a Korean fermented vegetable dish) may contain fish sauce, and some stews may include fish broth. While some fish sauces and fish stock are made from finned fish, others may include crustaceans, so it’s a good idea to avoid any foods made with these ingredients.

In addition, imitation crab is mainly made of a fish product called surimi but may contain small amounts of crab or crab extract, so you should avoid it unless you can confirm that there is no crab in the product. “At work today, I had a reaction to a seafood salad I was mixing for the deli,” one MyFoodAllergyTeam member wrote. “Checked the ingredients in the imitation crab we use to see if there were any components of real crab in it because that would explain the reaction.”

Meet With an Allergist

If you think you may have a crab or shrimp allergy, reach out to an allergist so they can perform allergy testing. If you’re allergic to crabs but not shrimp, your allergist may want to test you for shrimp anyway, just to be sure.

Talk With Others Who Understand

On MyFoodAllergyTeam, people share their experiences with food allergies, get advice, and find support from others who understand.

Have you ever experienced an allergic reaction after eating crab or shrimp? Let others know in the comments below.