Shellfish is the leading cause of self-reported food allergy in U.S. adults. It affects about 3% of adults and just over 1% of children.

People with a shellfish allergy can react to one or more foods in the same shellfish family. This is different than having an allergy to fin fish.

Some types of seafood look alike to the body. For instance, if you're allergic to one crustacean (like shrimp, crab, lobster), you're more likely to be allergic to another. Something similar is also seen with mollusks (like clam, oysters and mussels).

What causes shellfish allergies?

Food allergies are caused by an overreaction in your immune system. A food allergy occurs when the body mistakenly identifies a food substance (known as an allergen) as a foreign invader. This leads to an army of immune players working to remove the invader (known as a reaction). These reactions show up as an allergy.

There are many allergens that might cause shellfish allergy. The crustacean group, which includes shrimp, lobster and crab, causes the most reactions.

What are symptoms of shellfish allergy?

Shellfish allergy can cause a strong immune response. Within 60 minutes of eating the allergen, people with shellfish allergy can develop:

  • mouth and throat itching
  • lip swelling
  • skin reactions, such as hives, puffy eyes and skin redness

In some people, an allergic reaction to shellfish can be severe and life-threatening. This is called anaphylaxis. Symptoms may include:

  • coughing, wheezing, or trouble breathing due to constricted airways
  • severe abdominal pain
  • vomiting
  • diarrhea
  • low blood pressure
  • dizziness or fainting

In rare cases, the allergy can lead to death without immediate treatment with epinephrine. Epinephrine comes in many forms that can be injected or sprayed into the nose. EpiPen is just one of several options for allergy treatment. Each one works differently, so make sure to review with your pharmacist.

Watch this video from FARE (Food Allergy Research & Education) on how to use an EpiPen

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What are the standard diagnostic tests for shellfish allergy?

A health care provider starts off by reviewing the person's allergy history and making a referral to see an allergist. At the allergist's office, specialists review the patient's entire history.

The patient could undergo skin prick testing or blood testing to help confirm a shellfish allergy. However, these tests are not accurate in every situation. These tests cannot be used to predict a reaction. They can only confirm afterwards that a reaction was linked to a food.

Clinicians would then decide if an oral food challenge is needed to confirm a diagnosis. A food challenge is an office visit where the patient would eat the food in question in small amounts while being observed. Health professionals will monitor for any signs of reactivity and treat accordingly.

How long does it take shellfish allergy to go away, if at all? Do people outgrow shellfish allergy?

Most people do not outgrow shellfish allergies. In general, a small percentage of patients report outgrowing their allergy.

People who would like to know if they their allergy has resolved should see an allergist for further review. In the meantime, they should avoid the food that may be causing an allergy. They should also keep epinephrine on hand in the case of an accidental ingestion.

What role does immunotherapy play in treating allergies?

Oral and injection immunotherapies can decrease the sensitivity of patients to specific foods. They may lessen a reaction in case of accidental exposure to a food, but they do not cure a food allergy.

Patients who are on food-directed immunotherapy should still avoid the offending food outside of their treatment. They should also carry injectable or nasal epinephrine in case of accidental ingestion.

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What are some of the potential treatments for an allergic reaction?

In case of accidental ingestion, treatment of an allergic reaction is based on symptoms. Treatments include antihistamines, injectable epinephrine, and breathing treatments, if needed.

If you suspect an allergic reaction to a food, you should be evaluated by a medical professional. They can determine potential treatment and monitor symptoms going forward.

Corticosteroids (like prednisone or prednisolone) have not been shown to affect the treatment or outcome of an allergic reaction. Your provider can tell you if these may be useful.

Secondary therapies, like oral immunotherapy or biologic immunotherapies (Omalizumab), help suppress the severity of reactions. These are not used to treat immediate reactions or to cure food allergies.

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This blog was medically reviewed by pediatric allergist-immunologist Victoria Dimitriades, M.D.