Shellfish is the most common food allergy for adults in the United States. Almost 7 million people, or just over 2 percent of all Americans share this allergic reaction. Of those, approximately 60 percent develop their allergy to shellfish after they become adults.
Food allergy basics
A food allergy is a reaction by the body’s immune system. Normally, the body treats food as something that is beneficial. But when someone is allergic to a food, the body sees that allergen as a threat, like a bacteria or virus. This triggers the immune system to release antibodies to fight off the threatening particles. Depending on how severe the allergy is, food allergy symptoms can include hives, swelling around the mouth, itchy skin, runny nose, and stomach problems including nausea and diarrhea. The most serious allergic reaction is anaphylaxis, which is a full body reaction that can make the tongue and airway swell and cause a sudden drop in blood pressure. Anaphylaxis makes it hard to breathe and can result in death.
Shellfish allergy basics
Shellfish allergies include mollusks such as clams, mussels, and oysters as well as crustaceans which include shrimp, lobster, and crabs. Octopus and squid are also included in shellfish allergy.
For purposes of food allergy designations, fish are considered to be creatures with fins. Although fish and shellfish are separate allergies, many people who are allergic to shellfish are also allergic to fish. Allergic reactions to shellfish most commonly result in hives, redness and swelling under the skin, and anaphylaxis or swelling in the airways.
Foods to avoid
The most common cause of shellfish allergy is shrimp. But it is important to note that if you are allergic to any type of shellfish, there is a good chance you will be allergic to other shellfish as well as fish. The protein found in shellfish that most often causes allergies is also found in dust mites and cockroaches, so you may also be allergic to these insects.
In addition to avoiding each type of shellfish, be wary of products that often contain shellfish or that are prepared alongside shellfish:
• Supplements – Glucosamine, which is a supplement used to treat arthritis symptoms, is typically made from the shells of crustaceans. Most people are not allergic to the shell, but check with your doctor before you use this supplement or look for the vegetarian variety. Omega-3 supplements are often made from seafood so be sure to read the label.
• Sauces – Avoid Worcestershire sauce, some salad dressings, and other sauces containing shellfish.
• Imitation shellfish – Although this is not real shellfish, imitation shellfish often contains extracts from shellfish for flavoring.
• Asian foods – Many Asian foods including Chinese, Thai, Japanese, Vietnamese, and Malaysian contain shellfish or use fish sauces. Be careful of these types of restaurants where even a dish without shellfish may not be safe. Cross-contamination can occur if your dish is prepared in the same area, using the same utensils, or stored in the same refrigerator with shellfish, or if your plate touches a plate containing shellfish on the way to your table.
Read the labels
The only way to avoid contact with shellfish is to read the labels on all products that might contain shellfish. Because shellfish is one of the top eight food allergens in the United States, the Food and Drug Administration requires food manufacturers to clearly label all products containing shellfish. You need to be wary of products that are made by the same company as products containing shellfish. Cross-contamination can take place if foods that do not contain shellfish are prepared in the same facility, or using the same equipment, or are packaged on the same line as foods containing shellfish.
Sources:
About.com: Shellfish Allergy
The Food Allergy & Anaphylaxis Network
Mayo Clinic