Published on Thu, 03/19/2009 by Canadian Food Inspection Agency

Understanding Seafood Allergies


Allergic reactions to seafood occur when the body's immune system has an abnormal reaction to fish, crustaceans and/or shellfish.

What is the difference between crustaceans and shellfish?

Crustaceans are aquatic animals that have jointed legs, a hard shell and no backbone. This includes crab, crayfish, lobsters, prawns and shrimp.

Shellfish, on the other hand, include bivalve molluscs, which have a hinged two-part shell (for example, oysters, scallops, mussels and clams). Shellfish includesl other molluscs as well, such as whelk, snails, squid and octopus.

How can I avoid a fish, crustacean or shellfish-related reaction if I'm allergic to these foods?

Avoid all food and products that contain fish, crustacean or shellfish and their derivatives. This includes any product whose ingredient list warns it "may contain" or "may contain traces of" fish, crustaceans or shellfish.

What is the difference between a fish, crustacean or shellfish allergy, and histamine poisoning?

When someone has a seafood allergy, their immune system has an abnormal reaction to either fish, crustacean or shellfish proteins.

Histamine poisoning, on the other hand, is caused by eating fish that contain high levels of histamine, a chemical that forms when certain types of fish start to decompose.

High levels of histamine develop when fish, such as anchovies, mackerel, mahi-mahi and tuna, are not properly frozen or refrigerated. Histamine poisoning causes symptoms similar to seafood allergic reactions and can often be mistaken for a fish, crustacean or shellfish allergic reaction. If you are unsure whether you have a seafood allergy or histamine poisoning, consult an allergist or seek emergency medical treatment.

If I am allergic to one type of seafood will I be allergic to another?

It is possible for some people who are allergic to one type of seafood (fish, crustacean or shellfish) to eat other types of seafood without having a reaction. However, studies show that when a person has a specific seafood allergy, they may also be allergic to other species within the same group.

For example

- If you're allergic to cod, you may also be allergic to pike, as both are fish.
- If you're allergic to shrimp, you may also be allergic to lobster, as both are crustaceans.
- If you're allergic to mussels, you may also be allergic to clams, as both are shellfish.

If someone is allergic to one type of seafood—fish or crustaceans or shellfish—they will not necessarily be allergic to the other types. Consult your allergist before experimenting.

Can I have a seafood-related reaction even if I do not eat or use seafood and seafood derivatives?

Yes. There have been reported reactions to seafood vapours from fish, crustaceans and shellfish and/or products that contain them. This can happen from cooking, preparing (for example, sizzling skillets) and handling these products. Avoid these situations.

Seafood and seafood derivatives can often be present under different names, such as kamaboko. Always read the product ingredient list carefully.

What do I do if I am not sure whether a product contains seafood or seafood derivatives?

If you have a seafood allergy, do not eat or use the product. Get ingredient information from the manufacturer or importer.

If you or anyone you know has food allergies or would like to receive information about food being recalled, sign up for the Canadian Food Inspection Agency's free email "Food Recalls and Allergy Alerts" notification service available at

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