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Overview

Shellfish is among the most common food allergens. A shellfish allergy is different from an allergy to fish. Those who are allergic to shellfish do not necessarily have to avoid fish, and vice versa.

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Symptoms

Within the shellfish family, the crustacean group (shrimp, lobster and crab) causes the greatest number of allergic reactions. Many shellfish-allergic people can eat mollusks (scallops, oysters, clams and mussels) with no problem. Still, anyone with shellfish allergy symptoms should consult an allergist before eating any other kind of shellfish. Shellfish are often stored together in restaurants and markets, so cross-contamination can occur.

Shellfish allergies most frequently develop in adulthood but can affect children.

Shellfish allergy symptoms

  • Vomiting
  • Stomach cramps
  • Indigestion
  • Diarrhea
  • Wheezing
  • Shortness of breath, difficulty breathing
  • Repetitive cough
  • Tightness in throat, hoarse voice
  • Weak pulse
  • Pale or blue coloring of the skin
  • Hives
  • Swelling, can affect the tongue and/or lips
  • Dizziness
  • Confusion

Shellfish allergy triggers

Within the shellfish family, it is the crustacean group (shrimp, lobster and crab) that causes the greatest number of allergic reactions. Many shellfish-allergic people can tolerate mollusks (scallops, oysters, clams and mussels).

Diagnosis

Diagnosing shellfish allergies can be complicated. Symptoms can vary from person to person, and an 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 are close to shellfish being cooked, 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 perform skin-prick tests and/or order a blood test (such as an ImmunoCAP test), 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 your 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, another testing option for food allergy, 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 one is conclusive. A positive test result to a specific food does not always indicate that you will react to that food when it’s eaten. A negative test is more helpful to rule out a food allergy. Neither test, by size of the skin test wheal or the level of IgE antibodies, necessarily predicts how severe your allergic reaction to shellfish will be.

An allergist may use these tests and your 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 gradually increasing amounts of the suspected allergy-causing food under strict supervision. Experienced personnel, 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.

Management and Treatment

Once a shellfish allergy is identified, the best management is to avoid the food. You need to carefully check ingredient labels of food products. You should learn other names for the foods you need to avoid to be sure not to eat them.

You must be extra-careful when you eat out. Waiters (and sometimes the kitchen staff) may not always know every dish’s ingredient list. Vapors may carry small particles of shellfish protein, so being close to where food is being prepared can potentially cause a dangerous reaction in sensitive individuals.

Fortunately, shellfish is an ingredient that is rarely “hidden” in foods. Shellfish may be found in fish stock, seafood flavoring (for example, crab extract), sushi and surimi. Crustacean shellfish is one of the eight allergens that fall under the labeling requirements of the Food Allergen Labeling and Consumer Protection Act of 2004. This means that manufacturers of packaged food items sold in the United States and containing crustacean shellfish or a crustacean shellfish-based ingredient must state, in clear language, the presence of crustacean shellfish in the product. (Note: Those regulations apply only to crustacean shellfish, such as shrimp, lobster and crab, and not to mollusks, such as oysters, scallops and clams.)

Anyone with a food allergy must understand how to read ingredient labels and practice avoidance measures. Your allergist can direct you to helpful resources, such as special cookbooks, patient support groups and registered dietitians, who can help you plan your meals.

Many people with food allergies wonder if their condition is permanent. There is no clear-cut answer. Over time, allergies to milk, eggs and soy may disappear. Allergies to peanuts, tree nuts, fish and shellfish typically last a lifetime. About one-third of children and adults with a food allergy eventually outgrow the allergy. But rates of naturally outgrowing food allergies will vary depending on the specific food allergen and the person.

Managing a severe food reaction with epinephrine

Shellfish is among the most common food allergens. But all food allergies can be dangerous.

Epinephrine is the first-line treatment for anaphylaxis, a severe whole-body allergic reaction that causes symptoms, including tightening of the airway. Anaphylaxis can occur within seconds or minutes of exposure to the allergen, can worsen quickly, and can be deadly.

Once a food allergy diagnosis is made, your allergist likely will prescribe an epinephrine auto-injector and teach you how to use it. Check the expiration date of your auto-injector, note the expiration date on your calendar and ask your pharmacy about reminder services for prescription renewals.

Be sure to have two doses available, as the severe reaction may recur. Epinephrine should be used immediately if you experience severe symptoms such as shortness of breath, repetitive coughing, weak pulse, generalized hives, tightness in the throat, trouble breathing or swallowing, or a combination of symptoms from different body areas such as hives, rashes or swelling on the skin coupled with vomiting, diarrhea or abdominal pain. Repeated doses of epinephrine may be necessary.

If you are uncertain whether a reaction requires epinephrine, use it right away, because the benefits of epinephrine far outweigh the risk that a dose may not have been necessary.

Common side effects of epinephrine may include temporary anxiety, restlessness, dizziness and shakiness. Rarely, the medication can lead to an abnormal heart rate or rhythm, a heart attack, a sharp increase in blood pressure and fluid buildup in the lungs, but these adverse effects are generally caused by errors in dosing which is unlikely to occur with use of epinephrine autoinjectors. Some people with certain pre-existing conditions might be at higher risk for adverse effects and should speak to their allergist about epinephrine use.

Your allergist will provide you with a written emergency treatment plan that outlines which medications should be administered and when (note that between 10 and 20 percent of life-threatening severe allergic reactions have no skin symptoms). Be sure you understand how to properly and promptly use an epinephrine auto-injector.

Once you have used your epinephrine auto-injector, immediately call 911 and tell the dispatcher that you used epinephrine and that more may be needed from the emergency responders.

Other medications, such as antihistamine and corticosteroids, may be prescribed to treat mild symptoms of a food allergy, but it is important to note that there is no substitute for epinephrine — this is the only medication that can reverse the life-threatening symptoms of anaphylaxis.

Managing shellfish allergies in children

Because shellfish allergy reactions, like other food allergy symptoms, can develop when a child is not with his or her parents, parents need to make sure that their child’s school, day care or other program has a written emergency action plan with instructions on preventing, recognizing and managing these episodes in class and during activities such as sporting events and field trips.

If your child has been prescribed an auto-injector, be sure that you and those responsible for supervising your child understand how to use it.

 

This page was reviewed and updated as of 2/13/2019.