Causes, Symptoms, Treatment & Tests For Shellfish Allergy

Submitted on March 27, 2012

Seafood allergies refer to a food allergy caused by exposure to or eating seafood with scales and bones (fish) or those without a backbone (invertebrates). If you are diagnosed with a shellfish allergy this means that shellfish (invertebrates) can cause an allergic reaction when eaten.

Shellfish include marine life such as:

  • Crustaceans - prawns, crabs, lobster, crayfish.
  • Molluscs - mussels, oysters, abalone, cockles.
  • Cephalopods - octopus, cuttlefish, squid, and calamari.
  • Gastropods - sea slugs.

For some people, a shellfish allergy may cause a reaction only when you eat a particular type of shellfish. For others, the allergic reaction may be more cross-reactive and cause an allergy when eating different or all types of shellfish. Shellfish allergies affect approximately 1% of the population, tend to be life long, and are more commonly found in adults rather than children.

Tests Recommended

If you suspect that you have a shellfish allergy, consult with your doctor for a confirmation. He will reach a diagnosis after a physical examination (to rule out any other medical conditions) and then recommend any or both of the following shellfish allergy tests -

  • Skin test - your skin is pricked and small quantities of shellfish are places at the exposed site. If you have an allergy, a rash or hive will develop at the test area on the skin.
  • Blood test or Radioallergosorbent (RAST Test) - Also known as an allergy screen test, this test measures your body's response to the proteins in shellfish. If the level of antibodies in your bloodstream increases after exposure to shellfish, you may be diagnosed with a shellfish allergy.


Food allergies mainly occur due to a faulty immune system. In the case of shellfish allergy causes, certain proteins present in the shellfish are mistakenly considered harmful by your body's immune system. This results in the release of certain chemicals such as histamine to protect your body from these 'harmful' allergens. These chemicals or antibodies are the major cause of the allergy symptoms or allergic reaction.

Different kinds of shellfish contain different types of proteins that can cause reactions such as itchy eyes and nose, skin rashes, nausea, and breathing difficulties.


Shellfish allergy symptoms tend to develop immediately after eating shellfish. Typical signs of shellfish allergy would include:

  • Swelling of the face, lips, throat and tongue as well as other major parts of the body
  • Itching, Hives or eczema
  • Nasal congestion, difficulty breathing, wheezing
  • Diarrhea, nausea or vomiting
  • Stomach pain, cramping
  • Dizziness, fainting, lightheadedness
  • A tingling sensation in the mouth

If you find yourself responding adversely every time you eat any shellfish, consult with your doctor to reach a proper diagnosis.

For some, the allergic reaction may be so severe that a life-threatening condition known as anaphylaxis may develop.

Anaphylaxis is a reaction where your breathing gets impaired and requires immediate medical attention. Other signs of an anaphylactic reaction include constriction to your throat and airways, sharp fall in blood pressure, dizziness, rapid pulse, shock, and / or loss of consciousness. If you or anyone you know exhibits any of these symptoms, it is imperative to get to an emergency room at the earliest. The condition is a medical emergency and requires treatment with an epinephrine injection as soon as possible.


The best treatment for a shellfish allergy is to prevent the reaction from happening in the first place. You will need to avoid shellfish (and products containing shellfish) completely. Once you have tested for a shellfish allergy, your doctor may be able to definitely pin point the kind of shellfish causes the allergic reaction. In such cases, you need only to avoid this particular kind of shellfish. Unfortunately, for most people suffering from allergies to shellfish, all types of shellfish have to be avoided. People with a shellfish allergy however can eat fish of all types.

Special care has to be taken if you have any type of food allergy. Some suggestions if you suffer from a shellfish allergy include:

  • When eating out, stay alert of the fact that many restaurants use the same oil to fry shrimp, French fries or chicken.
  • Products sold as 'imitation' shellfish may still have some amount of real shellfish as a flavoring agent.
  • Read all food labels to be completely sure that your food is safe for consumption. Different types of seafood / shellfish are also found in foods such as sauces, salad dressing, soups, stock, Asian food, dips, chips and crackers, and even some food supplements.
  • Products such as fish fingers, fish nuggets or fish burgers could also contain processed shellfish parts so extra caution should be taken in such cases.
  • Stay away from buffets where you may be exposed to vapor from seafood / shellfish being served or cooked.
  • Some people react to even touching shellfish so care has to be taken at food markets and restaurants.

In case you do eat shellfish by mistake or come into contact with any type of shellfish, there are ways to treat the allergic reactions that may develop. In mild cases, allergic reactions such as skin rash or a runny nose can be treated with medications such as antihistamines. These will reduce the allergic symptoms and relieve any discomfort. Keep in mind though that antihistamines cannot be taken as a preventative measure against an allergic reaction. Rather they should be taken only after exposure to shellfish to control any symptoms.

For severe reactions to shellfish, you will require an emergency epinephrine (adrenalin) injection to counter the possibility of anaphylactic shock. If you are prone to severe allergic reactions, your doctor may recommend that you carry injectable epinephrine at all times in case of any emergency.