What is shellfish allergy?

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.

How common is shellfish allergy?

Shellfish is among the most common food allergens. It is also one of the most dangerous, sending more food-allergic people to hospital emergency rooms than any other. Please discuss with your doctor for further information.


What are the symptoms of shellfish allergy?

The common symptoms of shellfish allergy are:

  • 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

There may be some symptoms not listed above. If you have any concerns about a symptom, please consult your doctor.

When should I see my 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.


What causes shellfish allergy?

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.

Risk factors

What increases my risk for shellfish allergy?

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

Though people of any age can develop a shellfish allergy, it’s more common in adults. Among adults, shellfish allergy is more common in women. Among children, shellfish allergy is more common in boys.

Diagnosis & treatment

The information provided is not a substitute for any medical advice. ALWAYS consult with your doctor for more information.

How is shellfish allergy diagnosed?

Diagnosing shellfish allergies can be as complicated as the medical condition itself. Symptoms can vary from person to person, and a single individual may not always experience the same symptoms during every reaction. What’s more, people who are allergic to shellfish don’t necessarily have to eat it to develop a reaction. They may react if they simply breathe fumes, or if their food came in contact with shellfish.

Allergic reactions to shellfish can affect the skin, respiratory tract, gastrointestinal tract and/or cardiovascular system. While shellfish allergies most commonly aren’t seen until adulthood, the condition can appear at any age.

When a food allergy is suspected, it’s important to consult an allergist, who can determine which tests to perform, decide if an allergy exists and counsel patients on managing exposure and symptoms once the diagnosis has been confirmed.

To make a diagnosis, allergists ask detailed questions about the history of allergy symptoms. Be prepared to answer questions about what and how much you ate, how long it took for symptoms to develop, which symptoms you experienced and how long the symptoms lasted. The allergist will usually order a blood test (such as an ImmunoCAP test) and/or perform skin-prick tests, which indicate whether food-specific immunoglobulin E (IgE) antibodies are present in your body.

Skin-prick tests are conducted in a doctor’s office and provide results within 15 to 30 minutes. A drop of a liquid containing the suspected allergen is placed on the patient’s forearm or back. The skin is then pricked with a small, sterile probe, allowing the liquid to seep under the skin. The tests, which are not painful but can be uncomfortable, are considered positive if a wheal (resembling a bump from a mosquito bite) develops at the site.

Blood tests, which are less sensitive than skin-prick tests, measure the amount of IgE antibody to the specific food(s) being tested. Results are typically available in about one to two weeks and are reported as a numerical value.

Your allergist will interpret these results and use them to aid in a diagnosis. While both of these diagnostic tools can signal a food allergy, neither is conclusive. A positive test result to a specific food does not always indicate that a patient will react to that food when it’s eaten. A negative test is more helpful to rule out a food allergy. Neither test, by the level of IgE antibodies or the size of the wheal, necessarily predicts the severity of an allergic reaction to shellfish.

An allergist may use these tests and the patient’s history to make a food allergy diagnosis. For a definitive diagnosis, the allergist may wish to conduct an oral food challenge, in which the patient is fed tiny amounts of the suspected allergy-causing food in increasing doses over a period of time, under strict supervision. Emergency medication and emergency equipment must be on hand during this procedure.

Oral food challenges also may be performed to determine if a patient has outgrown a food allergy.

How is shellfish allergy treated?

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.

Your doctor may instruct you to treat a mild allergic reaction to shellfish, with medications such as antihistamines to reduce signs and symptoms, such as rash and itchiness.

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 having a severe reaction, carry injectable epinephrine (EpiPen, Auvi-Q, others) with you at all times. If you’re at risk for anaphylaxis to shellfish, your doctor may instruct you to administer epinephrine even at the first sign of an allergic reaction. After you use epinephrine, seek emergency medical care.

Lifestyle changes & home remedies

What are some lifestyle changes or home remedies that can help me manage shellfish allergy?

The following lifestyles and home remedies might help you prevent shellfish allergy:

  • Ask the staff how food is prepared when eating in a restaurant. Asian restaurants often serve dishes that contain fish sauce as a flavoring base. A shellfish-based broth or sauce may trigger an allergic reaction. Make sure to ask that the oil, pan, or utensils used to cook shellfish aren’t also used to prepare other foods. Stay away from steam tables or buffets.
  • Avoid eating at a seafood restaurant or shopping in a fish market. Some people react even if they inhale steam or vapor from cooking shellfish. Cross-contamination also is possible in establishments that serve seafood.
  • Read food labels carefully. Companies are required to disclose whether their food product contains shellfish. However, they aren’t required to disclose if the product contains mollusks, like scallops and oysters. Be cautious of foods that contain vague ingredients, like “fish stock” or “seafood flavoring.” Shellfish also may be present in many other dishes and substances, such as:
    • Surimi
    • Glucosamine
    • Bouillabaisse
    • Worcestershire sauce
    • Caesar salads
  • Let people know. When flying, contact the airline in advance to find out whether any fish or shellfish dishes will be prepared and served on the flight. Tell your employer or your child’s school or day care about any allergies. Remind a host or hostess of your allergy when you reply to an invitation to a dinner party.

You should always carry your epinephrine pen and make sure it hasn’t expired. You or your child should wear a medical bracelet or necklace containing your allergy information.

If you have any questions, please consult with your doctor to better understand the best solution for you.

Hello Health Group does not provide medical advice, diagnosis or treatment.

Review Date: December 13, 2017 | Last Modified: December 13, 2017

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