Shellfish allergy is an abnormal response by the body's immune system to proteins in certain marine animals. Shellfish include marine animals with shells, such as shrimp, crab, oysters and lobster, as well as squid and scallops.
Some people with shellfish allergy react to all shellfish; others react to only certain kinds. Reactions range from mild symptoms â such as hives or a stuffy nose â to severe and even life-threatening.
If you think you have a shellfish allergy, talk to your doctor. Tests can help confirm the allergy so you can take steps to avoid future reactions.
Shellfish allergy symptoms generally develop within minutes to an hour of eating shellfish. They may include:
Allergies can cause a severe, potentially life-threatening reaction known as anaphylaxis. An anaphylactic reaction to shellfish or anything else is a medical emergency that requires treatment with an epinephrine (adrenaline) injection and a trip to the emergency room.
Signs and symptoms of anaphylaxis include:
Seek emergency treatment if you develop signs or symptoms of anaphylaxis.
See a doctor or allergy specialist if you have food allergy symptoms shortly after eating.
All food allergies are caused by an immune system overreaction. In shellfish allergy, your immune system mistakenly identifies a certain protein in shellfish as harmful, triggering the production of antibodies to the shellfish protein (allergen). The next time you come in contact with the allergen, your immune system releases histamine and other chemicals that cause allergy symptoms.
There are several types of shellfish, each containing different proteins:
Some people are allergic to only one type of shellfish but can eat others. Other people with shellfish allergy must avoid all shellfish.
Your doctor will ask about your symptoms and may perform a physical exam to find or rule out other medical problems. He or she may also recommend one or both of the following tests:
A history of allergic reactions shortly after exposure to shellfish can be a sign of a shellfish allergy, but allergy testing is the only sure way to tell what's causing your symptoms and to rule out other possibilities, such as food poisoning. Medically supervised food challenges can be performed if any uncertainty remains about the diagnosis.
In severe cases, shellfish allergy can lead to anaphylaxis, a dangerous allergic reaction marked by a swollen throat (airway constriction), rapid pulse, shock, and dizziness or lightheadedness. Anaphylaxis can be life-threatening.
When you have shellfish allergy, you may be at increased risk of anaphylaxis if:
Anaphylaxis can be treated with an emergency injection of epinephrine (adrenaline). If you are at risk of having a severe allergic reaction to shellfish, you always should carry injectable epinephrine (EpiPen, Adrenaclick, others).
If you have a shellfish allergy, the only way to avoid an allergic reaction is to avoid all shellfish and products that contain shellfish. Even trace amounts of shellfish can cause a severe reaction in some people.
Read labels. Cross-contamination can occur in stores where other food is processed or displayed near shellfish and during manufacturing. Read food labels carefully.
Shellfish is rarely a hidden ingredient, but it may be in fish stock or seafood flavoring. Companies are required to label any product that contains shellfish or other foods that often cause allergic reactions, but the regulations don't apply to mollusks, such as clams, oysters and scallops.
If you have a shellfish allergy, talk with your doctor about carrying emergency epinephrine. Consider wearing a medical alert bracelet or necklace that lets others know you have a food allergy.
One thing you don't need to worry about is if you'll also be allergic to iodine or radiocontrast dye that's used in some imaging tests. Even though shellfish contain small amounts of iodine, shellfish allergy is unrelated to the reactions some people have to radiocontrast material or iodine.
You're at increased risk of developing a shellfish allergy if allergies of any type are common in your family.
Though people of any age can develop a shellfish allergy, it's more common in adults. Among adults, shellfish allergy is more common in women. Among children, shellfish allergy is more common in boys.