Shellfish
Allergy Facts, Symptoms, and Treatment

The most common cause of food allergy in adults, shellfish comprises more than 300 edible species, which are divided into two major groups, namely crustaceans and mollusks.1-3 Causing the greatest number of allergic reactions, crustaceans include various species such as crabs, lobsters, crayfish, prawns, shrimp, and krill.1,4 Meanwhile, there are three types of mollusks: bivalves (e.g., mussels, oysters, scallops, and clams), gastropods (e.g., limpets, periwinkles, and snails), and cephalopods (e.g., squid, octopus, and cuttlefish).1

Shellfish are eaten as raw and cooked meat, and various shellfish products are widely used as flavorings in packaged and processed food.2 In addition, shellfish skeletons and shells are employed to create a host of products, such as glucosamine, moisturizers, and calcium supplements.1 Although shellfish is a rich source of protein and omega-3 fatty acids, it's among the top eight food allergens in the United States, and shellfish allergy affects roughly 2 percent of the global population.2

Unfortunately, shellfish allergies typically last a lifetime, and carry one of the highest rates of food induced anaphylaxis.2,3 In fact, for adults and older children, shellfish are the leading cause of anaphylaxis in Thailand, Taiwan, Hong Kong, and Singapore.5 Shellfish allergy can occur in children, but 60 percent of allergic individuals experience their first related reactions as adults.1,3 Since people who react to one type of shellfish are likely to react to other members of the same group (i.e., crustaceans or mollusks), there is a high risk of reactions due to cross-contamination, which can easily occur in fish markets and during fish preparation.1

Where are shellfish found?

Shellfish are widely used as flavorings in packaged and processed food, and their shells and skeletons are employed to create a host of products, such as glucosamine, moisturizers, and calcium supplements. Allergic individuals may also experience allergy symptoms when they're near shellfish that's being cooked or processed, which is likely due to a reaction to aerosolized shellfish particles or vapors.1 As such, reactions have been reported among seafood industry workers, and allergic individuals may experience symptoms in environments where seafood is actively cooking, such as restaurants and kitchens.1,4

Since people who react to one type of shellfish are likely to react to other members of the same group (i.e., crustaceans or mollusks), there is a high risk of reactions due to cross-contamination, which can occur in fish markets and during fish preparation. This hazard also extends to frying oils. For example, if French fries (chips) were fried in the same oil as shrimp, the oil could contain traces of shellfish proteins, which can be passed along to the French fries.1

On food labels, shellfish may be identified as such, or it may be listed as any of the following, which may contain shellfish proteins.2

  • Crustaceans: barnacle, crab, crawfish, crevette, krill, lobster, Moreton bay bugs, prawns, shrimp (aka crevette, scampi)
  • Mollusks: abalone, clam, cockle, cuttlefish, limpet, mussel, octopus, oyster, periwinkle, sea cucumber, sea urchin, scallop, snail, squid (aka calamari), whelk

In addition, shellfish is sometimes found in the following:1,2 bouillabaisse, clam broth, condiments, crab extract powder, cuttlfish ink, etouffee, fish sauce, fish stock, fritto misto, glucosamine, fish stock, gumbo, jambalaya, lobster extract powder, kedgeree (a fish and rice dish), Lancashire hotpot (an English stew), oyster juice powder, oyster sauce, paella, scallop extract powder, seafood flavoring (e.g., crab or clam extract), shrimp powder, spices, and surimi.

Prepare for your next visit with your healthcare provider. 

Fill out our symptom tracker

Learn about specific IgE allergy testing options.

Read more

Are there other allergens I could be sensitized to?*

Some people with shellfish allergy may also experience symptoms when eating other seemingly unrelated foods. This is called cross-reactivity and occurs when your body's immune system identifies the proteins, or components, in different substances as being structurally similar or biologically related, thus triggering a response. The most common cross-reactivities with shellfish are other crustaceans (e.g., lobster, shrimp, and crab), and weaker cross-reactivity is found with mollusks (e.g., scallops, mussels, oysters, and squid). Plus in rare cases, dust mites and insects (such as cockroaches) may also be cross-reactive.2

Do I need to avoid all forms of shellfish?

Rather than destroying allergens in shellfish, heat processing and pressure treatment may enhance allergenic activity. As such, cooked shellfish may actually be more allergenic than raw iterations.2 Since shellfish and fish are not closely related species, being allergic to shellfish doesn t mean you're automatically allergic to finned fish. That said, given the risk for cross-contamination between fish and shellfish, exert caution when consuming fish that may have been exposed to shellfish.4

Shellfish consists of different types of proteins that all have different characteristics and different levels of risk for causing symptoms.2 Knowing the proteins, or components, within each allergen that are triggering your symptoms can help guide your management plan. With that in mind, and based on your symptom history, your healthcare provider may suggest something called a specific IgE component test, which can help reveal the risk profile you belong to.2

Already have your specific IgE component test results?

Your component test results will include the name of the components (a series of letters and numbers and/or name). Your healthcare provider will likely review the results with you, but here you'll find an at-a-glance breakdown you can use as a reference. Simply match the component names to the list below to see what they mean in terms of symptom management.2

rPen a 1 (tropomyosin)

  • Ingesting shellfish or mollusks may cause severe reaction, even anaphylaxis.
  • Inhaling aerosol or dust or having skin contact may cause reactions.
  • Other shellfish and crustaceans such as shrimp, crab, lobster, snail, and mollusks, as well as dust mites, may cause symptoms due to cross-reactivity.
  • Highly heat stable, meaning both raw and extensively cooked food may cause symptoms.

Test results should be interpreted by your healthcare provider in the context of your clinical history. Final diagnosis and decision on further management is made by your healthcare provider.

*These products may not be approved for clinical use in your country. Please work with your healthcare provider to understand availability.

How do I manage my allergy?

Because there is no cure for food allergies, your healthcare provider may recommend a plan that includes the following.1,4,8-11

  • Proceed with caution in environments where shellfish is being actively cooked or processed, such as restaurants and kitchens, and research potential cross-contamination sources before consuming shellfish.
  • Inquire about cross-contamination with frying oils. If shellfish has been fried in an oil, it may retain trace amounts of shellfish protein, which can be passed on to other food items fried in the same oil.
  • Read ingredient labels and "may contain" advisory panels on food and nonfood products carefully, and avoid all foods and products containing any form of the allergen. Note that these lists and panels may not appear on the same side of a product's packaging and that manufacturers frequently change ingredients. If you're unable to obtain a list of ingredients, it's safest to avoid that item.
  • Avoid cross-contamination when cooking by using two sets of cooking and eating utensils, with one exclusively for the allergic individual. Wash all dishes and utensils in hot soapy water between uses.
  • Craft an action plan with a list of steps for you and others to take should you accidentally ingest the allergen. Print out a copy of the plan and carry it with you.
  • Talk with restaurant chefs about your allergy and order food that's simply prepared and void of any form of the allergen. Avoid desserts, as they often contain or have come into contact with food allergens.
  • Plan ahead for traveling to ensure your food allergy will be managed and any emergency medication is always available.
  • Wear a medical ID bracelet identifying the allergen to which you're allergic.
  • Carry any recommended or emergency medication with you at all times.
  • Teach children with food allergies which foods to avoid. Work with caregivers and school staff to eliminate or reduce exposure to the allergen and to ensure they understand when and how to use medication to treat symptoms.

Your healthcare provider may direct you to take one of the following medications:

  • Epinephrine auto-injector when there are signs of an acute severe event, aka anaphylaxis (see below). Ensure your family members know how to administer it in case of an emergency.
  • Antihistamines as a supplement may be useful in relieving mild symptoms (e.g., itch); however, they do not halt the progression of an allergic reaction.
  • Bronchodilator (albuterol) as a supplemental therapy for respiratory symptoms, especially in those with a history of bronchospasm or asthma.

If you're with someone who's having an allergic reaction and shows signs of shock, act fast. Look for pale, cool, and clammy skin; a weak, rapid pulse; trouble breathing; confusion; and loss of consciousness. Do the following immediately:

  • Call local emergency services.
  • Ensure the affected individual is lying down with legs elevated.
  • Administer epinephrine immediately for any obvious signs of anaphylaxis.
  • Check the affected individual's pulse and breathing and administer CPR or other first-aid measures if necessary.

Looking for more allergy info and management tips?

Visit the Living with Allergies section
Download PDF

Shellfish Allergen Facts, Symptoms, and Treatment

Common Symptoms

Shellfish allergy can range from mild to severe and may vary over time, resulting in mild symptoms during one episode and severe symptoms in another. Although food allergy symptoms can start a few minutes to several hours after ingestion, most begin within two hours.6 Symptoms may involve the skin, gastrointestinal tract, cardiovascular system, and respiratory tract, and may include one or more of the following:6,7

  • Abdominal pain, diarrhea, nausea, vomiting, stomach cramps
  • Hives (allergic urticaria), itching, eczema
  • Wheezing, nasal congestion, shortness of breath, repetitive cough
  • Shock, circulatory collapse
  • Tight, hoarse throat, trouble swallowing
  • Pale or blue skin coloring
  • Dizziness, lightheadedness, fainting, weak pulse

Shellfish allergy symptoms can also include anaphylaxis, a whole-body reaction that can impair breathing, cause a dramatic drop in blood pressure, and affect heart rate. The most severe allergic reaction, anaphylaxis can come on within minutes of exposure and can be fatal.6 In fact, shellfish allergy, particularly to prawns, has one of the highest rates of food-induced anaphylaxis with nearly 42 percent among affected adults and 12 percent in children.2

Allergic individuals also may display symptoms when exposed to actively cooking shellfish. Caused by shellfish particles in the steam or vapors, allergic reactions typically elicit upper and lower respiratory symptoms, such as asthma, allergic rhinitis (aka hay fever), and skin problems.2

How do I know if I'm allergic?*

Together with your symptom history, skin-prick testing or specific IgE blood testing can help determine if you are allergic to a particular allergen. If you are diagnosed with an allergy, your healthcare provider will work with you to create a management plan.

*These products may not be approved for clinical use in your country. Please work with your healthcare provider to understand availability.

Is there a risk for a severe event?

Because food allergic reactions are unpredictable and symptoms range from local to systemic, it is recommended that an epinephrine prescription be considered for any patient with an IgE-mediated food allergy.8

If you have asthma, you may face a higher risk of severe shellfish reactions, particularly if your asthma is poorly controlled. Plus, if you have reacted to a very small amount of shellfish, you likely have a severe allergy.1

  1. The Anaphylaxis Campaign [Internet]. Farnborough, UK: The Anaphylaxis Campaign; 2019 Sep. Available from: https://www.anaphylaxis.org.uk/wp-content/uploads/2019/09/Shellfish-Sep-2019.pdf.
  2. EAACI, et al. Molecular allergology user's guide. Pediatr Allergy Immunol. 2016 May;27 Suppl 23:1-250. doi: 10.1111/pai.12563. PMID: 27288833. (225-234 p.) Available from: http://www.eaaci.org/documents/Molecular_Allergology-web.pdf.
  3. Food Allergy Research & Education [Internet]. McLean, VA: Food Allergy Research & Education; 2020. Available from: https://www.foodallergy.org/living-food-allergies/food-allergy-essentials/common-allergens/shellfish.
  4. American College of Allergy, Asthma & Immunology [Internet]. Arlington Heights, IL: American College of Allergy, Asthma & Immunology; 2019 Feb 13. Available from: https://acaai.org/allergies/types/food-allergies/types-food-allergy/shellfish-allergy.
  5. Loh W, Tang MLK. The Epidemiology of Food Allergy in the Global Context. Int J Environ Res Public Health. 2018 Sep 18;15(9):2043. doi: 10.3390/ijerph15092043. PMID: 30231558; PMCID: PMC6163515.
  6. American College of Allergy, Asthma & Immunology [Internet]. Arlington Heights, IL: American College of Allergy, Asthma & Immunology; 2014. Available from: https://acaai.org/allergies/types/food-allergy.
  7. Mayo Clinic [Internet]. Rochester, MN: Mayo Foundation for Medical Education and Research; 2019 Nov 2. Available from: https://www.mayoclinic.org/diseases-conditions/food-allergy/symptoms-causes/syc-20355095.
  8. Wright BL, Walkner M, Vickery BP, Gupta RS. Clinical Management of Food Allergy. Pediatr Clin North Am. 2015 Dec;62(6):1409-24. doi: 10.1016/j.pcl.2015.07.012. Epub 2015 Sep 7. PMID: 26456440; PMCID: PMC4960977
  9. American College of Allergy, Asthma & Immunology [Internet]. Arlington Heights, IL: American College of Allergy, Asthma & Immunology; 2014. Available from: https://acaai.org/allergies/types-allergies/food-allergy/food-allergy-avoidance.
  10. Harvard Health Publishing [Internet]. Boston, MA: Harvard Medical School; 2020. Available from:https://www.health.harvard.edu/healthbeat/6-tips-for-managing-food-allergies.
  11. Mayo Clinic [Internet]. Rochester, MN: Mayo Foundation for Medical Education and Research; 2019 Sep 14. Available from: https://www.mayoclinic.org/diseases-conditions/anaphylaxis/symptoms-causes/syc-20351468.
Our mission is to enable our customers to make the world healthier, cleaner and safer
© Thermo Fisher Scientific Inc. All Rights Reserved.