Why Is Shellfish an Allergen?

One of the most common food allergies is an allergy to shellfish. According to the Merck Manual Home Edition, older children and adults, as opposed to younger children, are the populations who are mostly allergic to shellfish. Shellfish are edible crustaceans such as lobster, shrimp, crab and crawfish. The allergy can also include mollusks such as oysters, clams, squid and snails. The allergy is caused by a protein found in these foods.

The Allergen Protein

• Mollusks, such as oysters, can also cause shellfish allergies.

  The reason some people are allergic to shellfish is because of a protein. The Mayo Clinic reports that the protein causes a malfunction in the immune system. This malfunction, in turn, causes the production of antibodies that are released to combat the protein (the protein is the allergen). The antibodies, which are composed of histamine and other chemicals, signal to the body that an allergen is present and symptoms develop, which is what is known as an allergic reaction. Each type of shellfish produces its own allergy-producing proteins.

Symptoms

• Shrimp shooters can be life threatening if you're allergic to shellfish.

  Depending on the severity of the allergy, symptoms may include skin reactions such as hives or rash, accompanied by swelling and itching. According to Beyond Allergy, these symptoms will occur within two to four hours after the shellfish has been eaten. More severe reactions are respiratory difficulties such as trouble breathing, asthma and congestion. In addition, the allergic reaction may trigger an upset stomach, nausea or diarrhea. According to the Merck Manual Home Edition, people with severe food allergies may want to keep the prescription antihistamine Cromolyn on hand to alleviate symptoms. The most severe allergic reaction, however, is known as anaphylaxis.

Anaphylaxis

• Prescription antihistamines can help relieve milder symptoms.

  Anaphylaxis is the medical term for a life-threatening allergic reaction. The Mayo Clinic reports that the symptoms include a swollen throat, quickened heart rate and dizziness. Because of the swelling of the throat, breathing may become compromised or completely shut off. There is an increased chance of having this type of reaction if asthma is already a problem. Because the problem can be life threatening, emergency treatment may be necessary. People who know they have a severe allergy to seafood need to consider keeping a special pen filled with epinephrine with them to combat the reaction.

Allergy Testing

• A blood test or skin test can detect specific allergies.

  As with determining other allergies, the physician will first inquire about symptoms and if a relationship to eating shellfish and an allergic reaction has occurred. There are two types of tests that can reveal an allergy to shellfish: a skin test and a blood test. The Mayo Clinic reports that the skin test is composed of pricking a small area on the skin, then introducing a tiny amount of the allergen proteins into the site. If any bumps or hives occur, the test is positive. The blood test consists of sending a traditional blood sample to a medical lab for analysis where an allergen-specific test is conducted.

Avioding the Allergy

• The one sure way to avoid an allergy to shellfish is to not eat it, although some people only have allergies to specific types of shellfish. According to Beyond Allergy, it is best to not consume any form of shellfish until a definitive allergy test has been conducted. Shellfish allergies can even occur just by handling the food, so this should be avoided as well, as should merely inhaling shellfish cooking fumes. Shellfish allergies last a lifetime, and there are no allergy shots that provide immunity.