Shellfish allergy

DEFINITION

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 octopus, squid and scallops.

Some people with shellfish allergy react to all shellfish; others react to only certain kinds. Reactions range from mild symptoms — such as hives or a stuffy nose — to severe and even life-threatening.

If you think you have a shellfish allergy, talk to your doctor. Tests can help confirm a shellfish allergy, so you can take steps to avoid future reactions.

CAUSES

All food allergies are caused by an immune system overreaction. Your immune system identifies a certain shellfish protein 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.

Types of shellfish

There are several types of shellfish, each containing different proteins:

• Crustaceans include crabs, lobster, crayfish, shrimp and prawn.
• Mollusks include squid, snails, octopus, clams, oysters and scallops.
• Some people are allergic to only one type of shellfish but can eat others. Other people with shellfish allergy must avoid all shellfish.

SYMPTOMS

Shellfish allergy symptoms generally develop within minutes to an hour of eating shellfish. They may include:

• Hives, itching or eczema (atopic dermatitis)
• Swelling of the lips, face, tongue and throat, or other parts of the body
• Wheezing, nasal congestion or trouble breathing
• Abdominal pain, diarrhea, nausea or vomiting
• Dizziness, lightheadedness or fainting
• Tingling in the mouth

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:

• A swollen throat or a lump in your throat (airway constriction) that makes it difficult for you to breathe
• Shock, with a severe drop in your blood pressure
• Rapid pulse
• Dizziness, lightheadedness or loss of consciousness

When to see a doctor

See a doctor or allergy specialist if you have food allergy symptoms shortly after eating. Seek emergency treatment if you develop signs or symptoms of anaphylaxis.