Shellfish Allergen Facts, Symptoms, and Treatment
Learn more about common allergic diseases, symptoms, management paradigms, and testing considerations.
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Learn more about common allergic diseases, symptoms, management paradigms, and testing considerations.
Is your patient a candidate for specific IgE testing?
Get detailed information on whole allergens and allergen components.
Ready to test a patient?
Access videos and webinars delivered by key experts in the field of allergy.
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
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
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.
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
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)
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.
Because there is no cure for food allergies, your healthcare provider may recommend a plan that includes the following.1,4,8-11
Your healthcare provider may direct you to take one of the following medications:
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:
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
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
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.
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