Peter had always loved seafood. So he was surprised one day when he noticed his mouth tingling after eating shrimp. He'd heard that people could get food allergies, but he didn't think he could have one because he'd always enjoyed shellfish with no problem.
The next time Peter ate shrimp, the reaction was more severe: His lips swelled up and he felt his throat tighten. Because his throat started to close up, his dad took him to the emergency room.
The ER doctor told Peter to avoid shellfish. She suggested he make an appointment with an allergist to find out if he had a shellfish allergy. Because shellfish allergies can be dangerous, knowing the signs of a shellfish allergy — and what to do if you have one — can make a big difference in preventing problems.
What Is a Shellfish Allergy?
You may hear people talk about having a "seafood" allergy or a "shellfish" allergy, but they don't mean the same thing. Here's the difference:
- 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 who has a shellfish allergy — unless that person also has a fish allergy.
- Shellfish fall into two different groups: crustaceans (like shrimp, crab, or lobster) and mollusks (like clams, mussels, oysters, scallops, octopus, or squid). Some people with shellfish allergies are allergic to both groups, but some might be allergic only to one.
People may outgrow some food allergies over time, but those with shellfish allergies usually have the allergy for the rest of their lives. Shellfish allergy can appear at any age. Even people who have eaten shellfish in the past can develop an allergy to it.
What Happens When Someone Has a Shellfish Allergy?
The body's immune system normally fights infections. But when someone is allergic to shellfish, the immune system overreacts to proteins in the shellfish. Every time the person eats shellfish, the body thinks these proteins are harmful invaders.
The immune system responds by kicking into high gear to fend off the "invader." This causes an allergic reaction in which chemicals like histamine are released in the body. In some cases, this reaction can even happen even if someone handles or breathes in airborne particles from shellfish.
The release of these chemicals can cause someone to have these symptoms:
- trouble breathing
- throat tightness
- itchy, watery, or swollen eyes
- red spots
- a drop in blood pressure, causing lightheadedness or loss of consciousness
People can have different reactions to different types of shellfish. It all depends on the person. Sometimes the same person can react in different ways at different times.
Shellfish allergies can cause a severe reaction called anaphylaxis. Anaphylaxis may begin with some of the same symptoms as a less severe reaction, but then quickly worsen, leading someone to have trouble breathing, feel lightheaded, or to pass out. If it is not treated, anaphylaxis can be life threatening.
What Can You Do?
If your doctor thinks you have a shellfish allergy, he or she will probably refer you to an allergist for testing. If test results come back positive, the allergist will give you advice on how to avoid shellfish.
The only real way to prevent allergic reactions is to avoid shellfish entirely. Avoiding a food you're allergic to means more than just not eating it. It also means not eating any foods that might contain shellfish ingredients. Plus, some non-food products (like pet foods, nutritional supplements, lip gloss, or plant fertilizer) sometimes contain shellfish ingredients. You'll need to read labels and be on the watch for those.
Most allergic reactions to shellfish happen when people eat shellfish, but sometimes people can react to touching shellfish or breathing in vapors from cooking shellfish. Some people can even get an allergic reaction from walking through a fish market!
Your allergist will give you a list of things to avoid. You also can check out the resources on the Food Allergy & Anaphylaxis Network website.
Reading Food Labels
Manufacturers of foods sold in the United States have to put on their labels if foods contain any of the most common allergens, including shellfish. When you see statements about shellfish on food labels, they are referring to crustacean shellfish. If you are allergic to mollusks, then you'll need to look for molluscan ingredients in the ingredients list.
In addition to finding out if foods have shellfish ingredients in them, you'll also want to be on the watch for cross-contamination. This can happen when a food you normally eat with no problems comes into contact with shellfish — like if a manufacturer uses the same equipment for lots of different foods or a restaurant uses a cutting board or pan to prepare both shellfish and other foods.
Food companies don't have to label for cross-contamination risk — though many do say things like "prepared in a facility that also processes shellfish." Avoid those foods. They may have shellfish proteins in them.
Since there's no requirement to label for cross-contamination, products without warning statements may be risky. So contact the company to see if a product could contain shellfish. You may be able to get this information from a company's website. If not, email the company to ask about cross-contamination risk.
If you're eating at a restaurant, cafeteria, friend's house, or anywhere else where you don't have control over how food is prepared, let the staff or hosts know you have a shellfish allergy.
Managing Serious Reactions
If doctors diagnose you with a life-threatening shellfish allergy (or any kind of life-threatening food allergy), they'll want you to carry an epinephrine auto-injector in case of an emergency. Epinephrine comes in an easy-to-carry container about the size of a large marker. It's simple to use — if you need to carry epinephrine, your doctor or an allergy nurse practitioner will show you how to use it.
Keep your epinephrine accessible at all times — not in your locker, but in a purse or bookbag that's with you. Be sure your school has injectable epinephrine where it's easy to get to. When it comes to anaphylaxis, seconds count. If your doctor has recommended you take other medications after an allergic reaction, keep them with you too.
If you accidentally eat something with shellfish in it and start having serious allergic symptoms, like swelling inside your mouth or throat or difficulty breathing, give yourself the shot right away.
After using epinephrine, call 911 for emergency help. Even after using epinephrine, people who have an anaphylactic reaction can have a second wave of symptoms after the initial attack. So you'll need to be under medical supervision at a hospital for several hours in case additional treatment is necessary.
Living with allergies can seem hard at times. But as more and more people are diagnosed with food allergies, schools, restaurants, and other businesses are more aware of the risks that those with food allergies face.
Reviewed by: Larissa Hirsch, MD
Date reviewed: September 2012
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