Shellfish Allergy

Shellfish allergy is one of the most common food allergies, affecting about 2 percent of people in the United States. It is most common in adults, but can also occur in children. Symptoms of shellfish allergy can range from hives, vomiting or nasal congestion to more-severe and even life-threatening symptoms. For some people, even a tiny amount of shellfish can cause a serious reaction.

Shellfish includes animals with shells, such as clams, lobster and shrimp, as well as octopus and squid. You may only be allergic to some kinds of shellfish, or you may need to avoid all shellfish. While over-the-counter and prescription medications can help control symptoms, the best way to prevent an allergic reaction is to avoid the type of food that causes it.

If you or your child has a reaction to shellfish, tell your doctor about it, no matter how mild the reaction may have been. Tests can help confirm a shellfish allergy, so you can take steps to avoid future and potentially more-severe reactions.

Shellfish allergy symptoms

Signs and symptoms of a shellfish allergy include:

  • Hives, itching or eczema
  • 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

A severe allergic reaction to shellfish called anaphylaxis is rare but can be life-threatening if it interferes with breathing. An anaphylactic reaction 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:

  • Constriction of airways, including a swollen throat or a lump in your throat, that makes it difficult to breathe
  • Shock, with a severe drop in blood pressure
  • Rapid pulse
  • Dizziness, lightheadedness or loss of consciousness
A shellfish allergy is distinct from an adverse reaction caused by toxins or bacteria. This type of food poisoning is common and can cause symptoms similar to a shellfish allergy. But unlike an allergy, it does not involve the immune system and only occurs when you eat food that has been contaminated. An allergic reaction to shellfish usually occurs every time you eat the type of shellfish that causes the reaction.

What causes it?

All food allergies are caused by an immune system malfunction. Your immune system identifies certain shellfish proteins as harmful, triggering the production of antibodies to neutralize the shellfish protein (allergen). The next time you come in contact with proteins in shellfish, these antibodies recognize them and signal your immune system to release histamine and other chemicals that cause allergy symptoms.

Histamine and other body chemicals cause a range of allergic signs and symptoms. Histamine is partly responsible for most allergic responses, including runny nose, itchy eyes, dry throat, rashes and hives, nausea, diarrhea, labored breathing, and in some cases, anaphylactic shock.

There are several types of shellfish, and each kind contains different allergy-causing proteins.

Crustaceans include crab, lobster, crayfish, shrimp and prawns.

Mollusks include:

  • Bivalves such as clams, mussels, oysters, scallops and abalone
  • Gastropods such as limpets, periwinkles and snails (escargot)
  • Cephalopods such as squid, cuttlefish and octopus
Some people are allergic to only one type of shellfish, but can eat others. However, some people with a shellfish allergy react to and must avoid all shellfish.
Also see Fish Allergy

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