A shellfish allergy causes an allergic reaction when you eat shellfish. Sometimes, a shellfish allergy is only to certain kinds of shellfish, or you may have an allergy to all shellfish. Shellfish include marine animals with shells, such as shrimp, crab, and lobster, as well as octopus and squid.
Shellfish allergy can cause mild symptoms, such as hives or nasal congestion, or more-severe and even life-threatening symptoms. For some people, even a tiny amount of shellfish can cause a serious reaction.
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.
Shellfish allergy symptoms generally develop within minutes of eating shellfish and include:
A severe allergic reaction to shellfish called anaphylaxis can be life-threatening if it interferes with your 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:
Though they share similar symptoms, a shellfish allergy is different from an adverse reaction to toxins or bacteria in your food. Unlike an allergy, food poisoning doesn't directly involve your immune system and occurs only 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.
When to see a doctor
All food allergies are caused by an immune system problem. Your immune system identifies certain shellfish proteins as harmful, triggering the production of antibodies to 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, difficulty breathing, and in some cases, anaphylactic shock.
There are several types of shellfish, and each kind contains different allergy-causing proteins.
Crustaceans include crabs, lobster, crayfish, shrimp and prawn.
Some people are allergic to only one type of shellfish, but can eat others. However, some people with a shellfish allergy must avoid all shellfish.
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 most common in adults. Among adults, shellfish allergy is more common in women. Among children, shellfish allergy is more common in boys.
In severe cases, shellfish allergy can lead to anaphylaxis, a dangerous allergic reaction marked by a swollen throat (airway constriction), rapid pulse, shock, and dizziness or lightheadedness. Anaphylaxis can be life-threatening.
When you have shellfish allergy, you may be at increased risk of anaphylaxis if:
Anaphylaxis can be treated with an emergency injection of epinephrine (adrenaline). If you are at risk of having a severe allergic reaction to shellfish, you should carry injectable epinephrine (such as an EpiPen) with you at all times.
Preparing for your appointment
You're likely to start by seeing your family doctor or a general practitioner. However, in some cases when you call to set up an appointment, you may be referred immediately to an allergy specialist.
What you can do
Questions related to shellfish allergy or other types of allergy may include:
What to expect from your doctor
What you can do in the meantime
Tests and diagnosis
Your doctor will ask about your symptoms and may perform a physical exam to find or rule out other medical problems. He or she may also recommend one or both of the following tests:
A history of allergic reactions shortly after exposure to shellfish can be a sign of a shellfish allergy, but allergy testing is the only sure way to tell what's causing your symptoms. Adverse reactions to shellfish are also sometimes caused by a nonallergic reaction, such as food poisoning or a bacterial or viral infection.
Treatments and drugs
The only sure way to prevent an allergic reaction to shellfish is to avoid shellfish altogether. Most people with a shellfish allergy can eat fish, however.
Despite your best efforts, however, you may still come in contact with shellfish. If you experience a mild allergic reaction to shellfish, medications such as antihistamines may reduce signs and symptoms, such as rash and itchiness. Antihistamines can be taken after exposure to shellfish to control your reaction and help relieve discomfort.
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 (such as an EpiPen, EpiPen Jr.) with you at all times.
Administer an emergency injection of epinephrine if you experience any of these symptoms after exposure to shellfish:
After you use epinephrine, seek emergency medical care.
If you know you're allergic to shellfish, the only sure way to avoid an allergic reaction is to avoid all shellfish or products that might contain shellfish. Even trace amounts of shellfish can cause a severe reaction in some people. Shellfish isn't usually a hidden food ingredient, so it may be easier to avoid than some other allergy-causing foods.
Some people mistakenly believe that allergy to iodine or allergy to radiocontrast dye used in some lab procedures can cause reactions in people with a shellfish allergy. Reactions to radiocontrast material or iodine are not related.
Glucosamine, a supplement used to prevent and treat arthritis, is made from crab, lobster or shrimp shells. While it does not appear to cause an allergic reaction in most people who have a shellfish allergy, more studies need to be done to determine whether it is safe for people allergic to shellfish.
If you are at risk of a serious allergic reaction, talk with your doctor about carrying emergency epinephrine (adrenaline). If you've already had a severe reaction, wear a medical alert bracelet or necklace that lets others know that you have a food allergy.
Last Updated: 2011-06-23
© 1998-2014 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.com," "Mayo Clinic Health Information," "Reliable information for a healthier life" and the triple-shield Mayo logo are trademarks of Mayo Foundation for Medical Education and Research.
Terms and conditions of use