Allergies: Shellfish

Overview

What is a shellfish allergy?

A shellfish allergy is a type of food allergy. If you have a shellfish allergy, you experience unpleasant symptoms after eating shellfish.

Shellfish are animals that live in the water and have a shell-like exterior. There are two types of shellfish:

  • Crustaceans: shrimp, crayfish, crab, lobster.
  • Mollusks: clams, scallops, oysters, mussels.

Is a shellfish allergy the same as shellfish intolerance?

An allergist can figure out if you are allergic to shellfish or have an intolerance. The difference matters. While an intolerance causes uncomfortable symptoms, an allergy can potentially be life-threatening.

Who gets shellfish allergies?

Anyone can develop a shellfish allergy — even if you’ve had shellfish before without any problems. Although it can occur at any age, it appears more often in adults than in children. About 60% of people who have a shellfish allergy first get symptoms as an adult. The reason may be that children typically don’t eat shellfish. People often eat shellfish for the first time as adults, which may be why symptoms appear later in life.

Is a shellfish allergy the same as a fish allergy?

No, shellfish allergies and fish allergies are different. You may have a shellfish allergy but be able to eat fish (and vice versa).

How common is a shellfish allergy?

A study found that approximately 2% of the population (around 6 million people) has a seafood allergy (meaning they are allergic to fish, shellfish or both).

Do all shellfish cause the same reaction?

Often, if you have an allergy to one type of shellfish, you will have an allergy to other types. Crustaceans cause more allergic reactions than mollusks.

You might have a reaction after eating lobster, for example, but eat scallops without a problem. If you have symptoms after eating shellfish, talk with your healthcare provider or allergist before eating any type of shellfish.

Shellfish allergies are sometimes confused with iodine allergies. That’s because shellfish often contains iodine. But having a shellfish allergy doesn’t necessarily mean you’re allergic to iodine. If you have a shellfish allergy, you don’t have to worry about reactions with radiocontrast material. (Certain diagnostic imaging scans use radiocontrast material, which contains iodine.)

What shellfish should I avoid if I have an allergy?

If you have a shellfish allergy, don’t eat these ingredients and foods:

  • Abalone.
  • Clams (such as cherrystone, littleneck, pismo, quahog).
  • Cockle.
  • Conch.
  • Crab.
  • Crawfish and crayfish.
  • Lobster.
  • Mollusks.
  • Mussels.
  • Octopus.
  • Oysters.
  • Scallops.
  • Shrimp and prawns.
  • Snails.
  • Squid (calamari).

Symptoms and Causes

What causes a shellfish allergy?

A shellfish allergy, or any food allergy, results from an immune system overreaction. Your immune system defends your body from invaders, such as infections. A food allergy occurs when your body identifies a food substance as a foreign invader and attacks it.

When do symptoms appear?

Typically, allergic reactions to food occur soon after eating the food — within a few minutes to a few hours.

What are symptoms of a shellfish allergy?

Shellfish allergy symptoms range from mild to severe. One person may experience itching and hives while another could have a life-threatening reaction, such as breathing problems. Symptoms can affect many different parts of the body: skin, respiration, digestion and heart.

Shellfish allergy symptoms include:

  • Itching.
  • Hives.
  • Eczema.
  • Tingling or swelling of the lips, tongue or throat.
  • Chest tightness, wheezing, coughing, shortness of breath and difficulty breathing.
  • Stomach issues: pain, nausea, indigestion, vomiting or diarrhea.
  • Dizziness, weak pulse or fainting.
  • Pale or blue skin coloring.
  • Anaphylaxis, a severe, potentially fatal allergic reaction, often involving several parts of the body.

Diagnosis and Tests

How is a shellfish allergy diagnosed?

Shellfish allergies can be challenging to diagnose. Symptoms differ from person to person, and the same person can have different reactions after eating shellfish. You may have a reaction without even eating shellfish — for example, if you’re cooking it or shellfish contaminates your food.

To diagnose a shellfish allergy, your healthcare provider (or allergist, a specialist in allergies) will ask you about your symptoms. You may need to answer:

  • What did you eat? And how much?
  • When did symptoms develop?
  • What symptoms did you have?
  • How long did symptoms last?

Will I need food allergy testing to diagnose a shellfish allergy?

After asking you about your symptom history, your provider may do food allergy testing to confirm a diagnosis:

  • Skin prick test: During this in-office test, your provider places a drop of the allergen on your skin and pricks your skin. The drop seeps into your skin. Your provider will confirm a diagnosis if a red, itchy bump appears after 15 to 30 minutes.
  • Blood test: A blood test can help detect whether you have a specific food allergy.

These tests are not conclusive. Together with your symptoms and history, your provider will make a diagnosis.

Will I need an oral food challenge?

This test can provide a definitive diagnosis. Under strict, careful supervision, you eat a small amount of the allergen. Your provider increases the dose gradually and notes your symptoms. Occasionally, allergists can use this test to see if you’ve outgrown the allergy. However, most people do not outgrow shellfish allergies.

Management and Treatment

How do I manage a shellfish allergy?

You can’t become “un-allergic” to shellfish. The best way to keep yourself healthy is to avoid shellfish. Besides avoiding shellfish itself, make sure you avoid foods that contain shellfish.

The Food and Drug Administration (FDA) requires food manufacturers to list common food allergens, such as shellfish, on food labels. The food label lists the allergen either in the ingredients list or after the list. For example, if a product contains abalone, a species of shellfish, the label will state “abalone (shellfish)” in the ingredients or “contains shellfish” after the ingredients list.

What treatments are used if I have an allergic reaction?

Epinephrine is the main treatment for anaphylaxis. Once your provider has confirmed a shellfish allergy, you will most likely get a prescription for self-injectable epinephrine (EpiPen®). Your provider will teach you how to use it.

If you have a severe allergic reaction and inject yourself with epinephrine, the next step is to call 911. Make sure to tell the dispatcher what happened and that you used your epinephrine injection. Emergency medical technicians (EMTs) may need to give you another dose when they arrive.

When should I use an epinephrine injection?

Use the injection right away if you notice:

  • Shortness of breath, coughing, weak pulse, hives, throat tightness or trouble breathing.
  • A combination of symptoms from different areas of the body, such as hives and swelling along with vomiting and diarrhea.

If I’m not sure my reaction is considered “severe,” should I inject myself with epinephrine?

In general, allergists recommend using the injection. The benefits of using it outweigh the risks of a potentially unnecessary dose.

What other medicines can treat a shellfish allergy?

If you have mild symptoms, your healthcare provider may recommend an antihistamine or corticosteroid. However, only epinephrine can treat the severe symptoms of anaphylaxis.

Prevention

How can I avoid an allergic reaction to shellfish?

The only way to avoid the negative effects of shellfish is to avoid shellfish entirely.

How else can I lower my risk for an allergic reaction?

In addition to not eating shellfish, these precautions can help you stay safe:

  • Try not to cook or touch shellfish: Particles can become airborne during cooking and cause an allergic reaction. Some people have a reaction from handling shellfish.
  • Use caution in seafood restaurants: Even non-shellfish dishes prepared in seafood restaurants may contain shellfish. Restaurants often use the same cooking equipment (and often, the same frying oil) for shellfish and non-shellfish dishes, so there may be contamination.

What other foods might contain shellfish?

These food items may contain shellfish as well, so avoid eating them:

  • Bouillabaisse, cioppino and other seafood stews.
  • Cuttlefish ink.
  • Fish stock.
  • Imitation fish.
  • Seafood flavoring.
  • Surimi.

Outlook / Prognosis

Is a shellfish allergy dangerous?

Any food allergy can be dangerous. Even if you’ve only experienced mild allergic symptoms to a food, you can always potentially have a dangerous reaction to that same food. It’s smart to be careful and prepared. Carry your epinephrine injection with you at all times. Note the expiration date so you can get a new one before it expires.

Does a shellfish allergy go away?

Most people who have a shellfish allergy have it for life. It does not go away over time.

Living With

If I have a shellfish allergy, how do I take care of myself?

You can live a healthy, enjoyable, active life with a shellfish allergy. Take some precautions to keep yourself healthy and feeling your best:

  • Know what you’re eating and drinking.
  • Check label ingredients — even if it’s a product you’ve eaten safely before. Often, manufacturers change recipes, and shellfish may have been added.
  • If your child is allergic, teach them not to accept food from friends.
  • Be restaurant safe: Ask detailed questions about ingredients and food preparation when you eat out.
  • Wear your medical alert bracelet or carry an alert card with you.
  • If your healthcare provider prescribed self-injectable epinephrine, carry it with you at all times. Make sure you have two doses available, as you may need to repeat the injection.

A note from Cleveland Clinic

A shellfish allergy can be annoying. It can interfere with your life, especially if you enjoy eating seafood. It’s smart to take precautions and avoid shellfish, even if you only experience mild symptoms. By avoiding shellfish, you can almost eliminate the uncomfortable (and potentially life-threatening) risks of an allergic reaction. If you notice symptoms after eating shellfish, talk to your healthcare provider or allergist to get a diagnosis. Your provider will talk to you about how to best care for yourself and explain how to use an epinephrine auto-injector.

Last reviewed by a Cleveland Clinic medical professional on 07/30/2020.

References

  • American College of Asthma, Allergies & Immunology. Accessed 7/30/2020.Shellfish Allergy. (https://acaai.org/allergies/types/food-allergies/types-food-allergy/shellfish-allergy)
  • Food Allergy Research & Education. Accessed 7/30/2020. Shellfish Allergy. (https://www.foodallergy.org/living-food-allergies/food-allergy-essentials/common-allergens/shellfish)
  • American Academy of Allergy, Asthma & Immunology. Accessed 7/30/2020.Shellfish Allergy Is Not a Shell Game. (https://www.aaaai.org/conditions-and-treatments/library/allergy-library/shellfish-allergy-can-be-dangerous)

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