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Shellfish allergy

Medically reviewed by Drugs.com. Last updated on Aug 5, 2022.

Overview

Shellfish allergy is an atypical response by the body's immune system to proteins in certain marine animals. Marine animals in the shellfish category include crustaceans and mollusks. Examples are shrimp, crabs, lobster, squid, oysters, scallops and snails.

Shellfish is a common food allergy. Some people with shellfish allergy react to all shellfish, while 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 shellfish allergy, talk to your health care provider. Tests can help confirm the allergy so you can take steps to avoid future reactions.

Symptoms

Shellfish allergy symptoms generally start within minutes to an hour after eating or having contact with shellfish. They may include:

Anaphylaxis

Allergies can cause a severe, potentially life-threatening allergic reaction known as anaphylaxis. It can occur within seconds to minutes after exposure to something you're allergic to — and worsens quickly.

An anaphylactic reaction to shellfish is a medical emergency. Anaphylaxis requires immediate treatment with an epinephrine (adrenaline) injection and a follow-up trip to the emergency room. If anaphylaxis isn't treated right away, it can be fatal.

Anaphylaxis causes the immune system to release a flood of chemicals that can cause you to go into shock. Signs and symptoms of anaphylaxis include:

When to see a doctor

Seek emergency treatment if you develop signs or symptoms of anaphylaxis.

See a health care provider or allergy specialist if you have food allergy symptoms shortly after eating.

Causes

All food allergies are caused by an immune system overreaction. Your immune system identifies a harmless substance as being harmful. This substance is called an allergen. In shellfish allergy, your immune system mistakenly identifies a certain protein in shellfish as harmful. Your immune system is how your body protects itself, so it produces immunoglobulin E (IgE) antibodies to protect against this allergen. The next time you come in contact with the shellfish protein, these antibodies signal your immune system to release chemicals such as histamine into your bloodstream. This causes a reaction that leads to the symptoms of an allergic reaction.

Types of shellfish

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

An allergy to crustaceans is the most common type. Some people are allergic to only one type of shellfish but can eat others. Other people with shellfish allergy must avoid all shellfish.

An allergy to fish — such as salmon, tuna or catfish — is a different seafood allergy from an allergy to shellfish. Some people who are allergic to shellfish may still be able to eat fish, or they could be allergic to both. Your health care provider can help you determine what is safe to eat.

Risk factors

You're at increased risk of developing shellfish allergy if allergies of any type are common in your family.

Though people of any age can develop shellfish allergy, it's more common in adults. In fact, shellfish allergy is the most common food allergy in adults. Among adults, shellfish allergy is more common in women. Among children, shellfish allergy is more common in boys.

Complications

In severe cases, shellfish allergy can lead to anaphylaxis, a dangerous allergic reaction that can be life-threatening.

When you have shellfish allergy, you may be at increased risk of anaphylaxis if you have:

Anaphylaxis is 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 (Auvi-Q, EpiPen, others).

Prevention

If you have 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.

Avoiding shellfish

Be prepared

If you have shellfish allergy, talk with your health care provider about carrying emergency epinephrine and how to use it.

Consider wearing a medical alert bracelet or necklace that lets others know you have a food allergy.

Iodine or radiocontrast dye

One thing you don't need to worry about is if you'll also be allergic to iodine or radiocontrast material 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.

Diagnosis

To find out if you have shellfish allergy, your health care provider will ask about your symptoms and do a physical exam to find or rule out other medical problems.

A history of allergic reactions shortly after exposure to shellfish can be a sign of shellfish allergy. But the symptoms could also be caused by something else, such as food poisoning.

Allergy testing is the only sure way to tell what's causing your symptoms, so your provider may recommend one or both of these tests:

Medically supervised food challenges can be performed if the diagnosis still isn't clear after allergy testing.

Positive reaction to allergy test

A small area of swelling with surrounding redness is typical of a positive allergy skin test.

Treatment

The only sure way to prevent an allergic reaction to shellfish is to avoid shellfish. But despite your best efforts, you may come into contact with shellfish.

If you have a severe allergic reaction to shellfish (anaphylaxis), you'll likely need an emergency injection of epinephrine (adrenaline). If you're at risk of anaphylaxis to shellfish, your health care provider can give you a prescription in advance and explain how and when to give the injection. Regularly check the expiration date on the packaging to make sure it's current.

Carry injectable epinephrine (Auvi-Q, EpiPen, others) with you at all times. Epinephrine is typically given at the first sign of an allergic reaction. A second dose may be needed if symptoms recur. After you use epinephrine, seek emergency medical care, even if you start to feel better.

Preparing for an appointment

You're likely to start by seeing your family health care provider. Or you may be referred directly to an allergy specialist.

What you can do

Prepare for your appointment by making a list of:

Questions related to shellfish allergy include:

Don't hesitate to ask other questions, as well.

What to expect from your doctor

Your health care provider may ask you questions, such as:

What you can do in the meantime

Avoid eating or touching any type of shellfish while waiting for your appointment.

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