Shellfish Allergy

About Shellfish Allergy

A shellfish allergy is not exactly the same as a seafood allergy. Seafood includes both fish (like tuna or cod) and shellfish (like lobster or clams). Even though they both fall into the category of "seafood," fish and shellfish are biologically different. So fish will not cause an allergic reaction in someone with a shellfish allergy — unless that person also has a fish allergy.

The two different types of shellfish allergy are:

  1. crustaceans (like shrimp, crab, or lobster)
  2. mollusks (like clams, mussels, oysters, or scallops)

Some people with shellfish allergies are allergic to both groups; some are allergic only to one. Although most allergic reactions to shellfish happen when someone eats shellfish, sometimes a person can react to touching shellfish or breathing in vapors from cooking shellfish.

Shellfish allergy can develop at any age. Even people who have eaten shellfish in the past can develop an allergy. Some people outgrow certain food allergies over time, but those with shellfish allergies usually have the allergy for the rest of their lives.

A shellfish allergy can cause a very serious reaction, even if a previous reaction was mild. So anyone with a shellfish allergy should completely avoid shellfish.

If your child has been diagnosed with a shellfish allergy, keep injectable epinephrine on hand in case of a severe reaction. This is a medicine that your doctor can prescribe. Communicate emergency plans with anyone who will be taking care of your child, including relatives and school officials. Also consider having your child wear a medical alert bracelet.

What Happens in a Shellfish Allergy

When someone is allergic to shellfish, the body's immune system, which normally fights infections, overreacts to proteins in the shellfish. Every time the person eats (or, in some cases, handles or breathes in) shellfish, the body thinks these proteins are harmful invaders.

The immune system responds by working very hard to fend off the invader. This causes an allergic reaction, in which chemicals like histamine are released in the body. The release of these chemicals can cause someone to have these symptoms:

  • wheezing
  • trouble breathing
  • coughing
  • hoarseness
  • throat tightness
  • stomachache
  • vomiting
  • diarrhea
  • itchy, watery, or swollen eyes
  • hives
  • red spots
  • swelling
  • a drop in blood pressure causing lightheadedness or loss of consciousness

Your child could have different reactions to different types of shellfish or react differently at different times. Some reactions can be very mild and involve only one system of the body, like hives on the skin. Other reactions can be more severe and involve more than one part of the body.

Anaphylaxis Is a Life-Threatening Reaction

Shellfish allergies can cause a severe reaction called anaphylaxis. Anaphylaxis can begin with some of the same symptoms as a less severe reaction, but then can quickly worsen, leading someone to have trouble breathing or to pass out. If it is not treated, anaphylaxis can be life threatening.

If your child starts having serious allergic symptoms, like swelling of the mouth or throat or difficulty breathing, give the epinephrine auto-injector right away. Every second counts in an allergic reaction. Then call 911 or take your child to the emergency room. Your child needs to be under medical supervision because even if the worst seems to have passed, it's common for a second wave of serious symptoms to occur.

An epinephrine auto-injector is a prescription medicine that comes in an easy-to-carry container about the size of a large marker. It's simple to use. If your child needs to have it on hand, your doctor will show you how to use it. Kids who are old enough can be taught how to give themselves the injection.

Staff at your child's school should know that your son or daughter has a serious food allergy. You should agree upon a plan in case of a serious reaction and the injectable epinephrine must be available at all times. If your child is old enough to carry his or her own epinephrine, it should not be in a locker, but in a purse or backpack that's with your child at all times.

Your child's allergy plan also could include giving an over-the-counter antihistamine for milder allergy symptoms. But the antihistamine should be given after the epinephrine in the case of a serious, life-threatening reaction.

Shellfish Allergy Safety Tips

To prevent allergic reactions to shellfish, your child must not eat shellfish. He or she also must not eat any foods that might contain shellfish as ingredients. For detailed information, you can visit websites that your doctor recommends, such as the Food Allergies and Anaphylaxis Network.

Also, read food labels to see if a food is free of shellfish. Manufacturers of foods sold in the United States must state in understandable language whether foods contain any of the top eight most common allergens, including crustacean shellfish. The label should list "shellfish" in the ingredient list or say "Contains shellfish" after the list.

Also look for advisory statements such as "May contain shellfish," "Processed in a facility that also processes shellfish," or "Manufactured on equipment also used for shellfish." These are cross-contamination warnings, but manufacturers are not required to list them.

Since products without precautionary statements also might be cross-contaminated and the company simply chose not to label for it, it is always best to contact the company to see if the product could contain shellfish. You might find this information on the company's website or you can contact a company representative via email.

Manufacturers also do not have to list mollusk shellfish ingredients because mollusk shellfish (clams, mussels, oysters, or scallops) are not considered a major food allergen. When labels say a food contains shellfish, they refer to crustacean shellfish. Contact the company to see about cross-contamination risk with mollusks.

Even if a food did not cause a reaction in the past, it still could be a problem. Manufacturers may change processes or ingredients at any time.

Shellfish ingredients also might be used in some non-food products, like nutritional supplements, lip gloss, pet foods, and plant fertilizer. Talk to your doctor if you have questions about what is safe.

Cross-Contamination

Cross-contamination often occurs in restaurants, which is where many people often mistakenly eat shellfish. This happens in kitchens when shellfish gets into a food product because the staff use the same surfaces, utensils (like knives, cutting boards, or pans), or oil to prepare both shellfish and other foods.

This is particularly common in seafood restaurants, so some people find it safer to simply avoid these restaurants altogether. Since shellfish is also used in a lot of Asian cooking, there's a risk of cross-contamination in Chinese, Vietnamese, Thai, or Japanese restaurants. It's a good idea to avoid a restaurant's fried foods, like French fries and fried chicken, because the restaurant may use the same oil to fry shrimp.

Eating Away From Home

When your child eats in a restaurant or at a friend's house, find out how foods are cooked and exactly what's in them. It can be hard to ask a lot of questions about cooking methods, and to trust the information you get. If you can't be certain that a food is shellfish-free, it's best to bring safe food from home.

Also talk to the staff at school about cross-contamination risks for foods in the cafeteria. It may be best to pack lunches at home so you can control what's in them.

If your child will be eating at a restaurant, take these precautions:

  • Stay away from steam tables or stovetops when shellfish is cooked (especially places where food is cooked on a communal grill, like hibachi restaurants).
  • Tell the restaurant waitstaff that your child has as serious shellfish allergy.
  • Carry a personalized "chef card" for your child, which can be given to the kitchen staff. The card details your child's allergies for food preparers. Food allergy websites provide printable chef card forms in many different languages.
  • Don't eat at a restaurant if the manager or owner seems uncomfortable about your requests for a safe meal.

Reviewed by: Larissa Hirsch, MD
Date reviewed: September 2012