Seafood Allergy – Symptoms and Causes


Shellfish allergy is an atypical response of the body’s immune system to the proteins of certain marine animals. Marine animals in the shellfish category include crustaceans and molluscs. Examples are shrimp, crabs, lobster, squid, oysters, scallops and snails.

Shellfish are a common food allergy. Some people with shellfish allergies react to all shellfish, while others only react to certain types. Reactions range from mild symptoms, such as hives or a stuffy nose, to severe and even life-threatening symptoms.

If you think you may be allergic to shellfish, talk to your healthcare provider. Testing can help confirm the allergy so you can take steps to prevent future reactions.



Shellfish allergy symptoms usually begin minutes to an hour after eating or coming into contact with shellfish. They may include:

  • Urticaria
  • Itchy, irritated skin
  • Nasal congestion (stuffiness)
  • Swelling of the lips, face, tongue and throat or other parts of the body
  • Wheezing or difficulty breathing
  • Cough and choking or tightness in the throat
  • Abdominal (abdominal) pain, diarrhoea, nausea or vomiting
  • Dizziness, lightheadedness, or fainting


Allergies can cause a severe, life-threatening allergic reaction known as anaphylaxis. It can happen seconds to minutes after exposure to something you’re allergic to ⸺ and get worse quickly.

An anaphylactic reaction to shellfish is a medical emergency. Anaphylaxis requires immediate treatment with an injection of epinephrine (adrenaline) and a follow-up trip to the emergency room. If anaphylaxis is not treated immediately, it can be fatal.

Anaphylaxis causes the immune system to release a flood of chemicals that can cause shock. Signs and symptoms of anaphylaxis include:

  • A swelling of the throat or tongue or a feeling of tightness in the throat (constriction of the airways) that makes it difficult to breathe
  • Coughing, choking or wheezing with difficulty breathing
  • Shock, with a severe drop in your blood pressure and a rapid or weak pulse
  • Severe skin rash, hives, itching or swelling
  • Nausea, vomiting or diarrhea
  • Dizziness, lightheadedness, or fainting

When to consult a doctor

Seek emergency treatment if you develop signs or symptoms of anaphylaxis.

Consult a health care provider or allergy specialist if you experience food allergy symptoms shortly after eating.


All food allergies are caused by an overreaction of the immune system. Your immune system recognizes a harmless substance as harmful. This substance is called an allergen. In shellfish allergy, your immune system mistakenly identifies a certain protein in shellfish as harmful. Your immune system is your body’s way of protecting itself, so it produces immunoglobulin E (IgE) antibodies to protect against this allergen. The next time you come into contact with the shell protein, these antibodies signal your immune system to release chemicals such as histamine into your bloodstream. This causes a reaction that leads to the symptoms of an allergic reaction.

Types of shells

There are several types of shellfish, each containing different proteins:

  • Shellfish include crabs, lobster, crayfish, prawns and prawns
  • molluscs include squid, octopus, mussels, snails, clams, oysters, abalone and scallops

A shellfish allergy is the most common type. Some people are allergic to only one type of shellfish but can eat others. Other people with shellfish allergies should avoid all shellfish.

An allergy to fish ⸺ such as salmon, tuna or catfish ⸺ is a different seafood allergy than a shellfish allergy. Some people with a shellfish allergy may still eat fish or be allergic to both. Your healthcare provider can help you determine what is safe to eat.

Risk factors

You are at an increased risk of developing a shellfish allergy if allergies of any type are common in your family.

Although people of any age can develop a shellfish allergy, it is more common in adults. In fact, shellfish allergy is the most common food allergy in adults. In adults, shellfish allergy is more common in women. In children, shellfish allergy is more common in boys.


In severe cases, shellfish allergy can lead to anaphylaxis, a dangerous allergic reaction that can be life-threatening.

When you have a shellfish allergy, you may be at increased risk of anaphylaxis if you have:

  • Asthma
  • Allergic reactions to very small amounts of shellfish (extreme sensitivity)
  • History of foodborne anaphylaxis
  • Strong family history of allergy

Anaphylaxis is treated with an emergency injection of epinephrine (adrenaline). If you are at risk of having a severe allergic reaction to shellfish, you should always carry injectable epinephrine with you (Auvi-Q, EpiPen, others).


If you are allergic to shellfish, the only way to avoid an allergic reaction is to avoid all shellfish and products containing them. Even traces of shellfish can cause a severe reaction in some people.

Avoid shells

  • Be careful when dining out. When dining out, always check that the pan, oil or utensils used for shellfish are not also used to prepare other foods, creating cross-contamination. It may be necessary to avoid eating at seafood restaurants, where the risk of cross-contamination is high.
  • Read the labels. Cross-contamination can occur in stores where other foods are processed or displayed near shellfish and during manufacturing. Shellfish can be in fish broth or flavored with seafood. Read food labels carefully.

    Shellfish is usually not a hidden ingredient. Companies are required to label any product containing shellfish or certain other foods that often cause allergic reactions. However, these regulations do not apply to shellfish.

  • Keep your distance. You may need to completely avoid places where shellfish are prepared or processed. Some people react after touching shellfish or inhaling steam from cooking shellfish.

be ready

If you are allergic to shellfish, talk to your health care provider about carrying emergency epinephrine and how to use it.

Consider wearing a medical alert bracelet or necklace that lets others know you have a food allergy.

Iodine or radiocontrast dye

One thing you don’t have to worry about is whether you will also be allergic to iodine or the radiocontrast material used in some imaging tests. Although shellfish contain small amounts of iodine, shellfish allergy is not related to some people’s reactions to radiocontrast material or iodine.

August 05, 2022

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