Seafood allergy is one of the most common food allergies in the world, particularly, among adults in the U.S. It is much more common in adults than in children and once you develop this type of allergy, it tends to be severe and lifelong. Seafood allergy can also develop even though shellfish or fish was previously eaten without any problems.

The term “seafood” encompasses the following:

• Vertebrate finned fish such as salmon, tuna, and cod
• Crustaceans such as shrimp, prawn, crab, lobster, and crawfish
• Mollusks such as squid, snails, and bivalves (scallops, clams, oysters, mussels, among others)

People who are allergic to one type of crustacean are generally allergic to all other crustaceans as well, but there are others who react to only certain kinds. Reactions range from mild symptoms to severe and even life-threatening. Allergy testing is still the safest way to determine specifically which shellfish or seafood you’re allergic to.

Causes

In seafood allergy, the immune system reacts to a certain protein that it mistakenly identified as harmful, which then triggers the production of antibodies and causes allergy symptoms.

Symptoms

Allergy symptoms generally develop within minutes to an hour of eating shellfish. In severe cases, eating a small amount can even cause an anaphylactic reaction, which require immediate medical emergency. Common symptoms of seafood allergy may include:

• Hives, itching or eczema
• Swelling of the lips, face, tongue, throat, or other parts of the body
• Wheezing, nasal congestion, or shortness of breath
• Abdominal pain, diarrhea, nausea or vomiting
• Dizziness, lightheadedness or fainting

Symptoms of anaphylaxis include:

• Swollen throat
• Shock or a drop in your blood pressure
• Loss of consciousness

Not all seafood allergy is allergy

Allergies are not the only medical conditions related to seafood. There is shellfish poisoning, which is also called paralytic shellfish poisoning and red tide. It is caused by a very potent toxin called saxitocin, found in two-shelled mollusks such as clams and oysters. Symptoms of shellfish poisoning, which are sometimes mistaken for an allergic reaction, include a tingling or burning sensation in the mouth or extremities, nausea, vomiting and diarrhea, which is usually experienced within 30 minutes of eating tainted shellfish. These symptoms require emergency medical care.

Exposure

Aside from eating small amounts, to some sensitive individuals, even minimal exposure to seafood can cause symptoms. Handling fish or shellfish or inhaling fish or shellfish vapors in a fish market or restaurant can cause a reaction. Those with known seafood allergies need to be careful when these foods are being prepared, because fish and shellfish are the only foods known to significantly release the food protein into the air.

Diagnosis

The doctor will ask about your symptoms and perform a physical exam to rule out other medical problems. He or she will likely administer a skin test, in which the skin is pricked and exposed to small amounts of protein found in seafood. A raised bump at the test site indicates that you’re allergic. The other one is a blood test, or also called an allergen-specific IgE antibody test or radioallergosorbent (RAST) test, which measures the immune system’s response to shellfish proteins by measuring the amount of immunoglobulin E antibodies in the bloodstream.

Prevention

The following precautions can be taken to avoid triggering a reaction:

• Avoid contact with the food
• Always check the ingredients before using a product or eating any food
• Ask detailed questions about ingredients and how the food was prepared whenever you’re dining out
• Inform those around you about your food allergy
• Have an allergy action plan for treatment–know the medicines used to treat reactions and have them with you at all times

Managing your symptoms

Aside from totally avoiding seafood or shellfish, your doctor may recommend treating a mild allergic reaction with medications such as antihistamines to reduce signs and symptoms. For those with severe allergic reactions, an emergency injection of epinephrine will be performed.