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Useful facts on fish and shellfish (fisk og skalldyr)

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Fish and shellfish

Useful information concerning fish and shellfish – NAAF’s fact sheet

What is fish and shellfish allergy?

Allergy to fish results from a physical reaction to a protein in the fish meat. Most individuals allergic to fish react predominantly to fish belonging to the cod family. Some tolerate fish species such as salmon, trout, mackerel and herring fish, whilst some only react to red fish and tolerate for example, cod. Around half of those who are allergic to fish react to all types of fish.

The allergy-provoking agents in fish are very heat stable, which means that they do not disappear with boiling or cooking. Some sensitive individuals suffer allergic reactions if they breathe in the vapour from boiled fish. This vapour may cause asthma symptoms or allergic runny nose/eyes.

Shellfish allergy (prawns, lobster, crayfish and crab) may also be severe, and often lasts a lifetime. There is no correlation between fish allergy and allergy to shellfish, such that most of those who are allergic to shellfish can eat fish and vice versa. Exclusion of shellfish from the diet is relatively simple and does not represent any nutritional risk.

It is not uncommon for non-allergic individuals to experience skin reaction to the preparation or ingestion of shellfish. Such reactions are likely due to histamine release.

When do you get this allergy?

Fish allergy usually has onset relatively early in life, in conjunction with that fish is introduced into the diet. Shellfish allergy generally occurs somewhat later; this is likely due to the fact that shellfish is often not served before the child is a little older.

What reactions does fish and shellfish allergy produce?

Individuals with fish allergy may suffer asthma symptoms, intestinal/stomach symptoms, skin rashes and running eyes and nose. Some react with more serious symptoms, such as loss of blood pressure and breathing difficulties.

How is fish allergy treated?

Fish allergy is generally treated by excluding the non-tolerated foodstuff from the diet.

Which products contain fish and shellfish?

In addition to seafood dishes, some pre-prepared foods also contain fish or shellfish as ingredients. In particular, anchovies are often included in liver pâté, tapenade, Caesar dressing and Worcester sauce. Crab salad may contain fish, and crabsticks are made from fish, not shellfish. Oyster sauce or fish sauce is manufactured from, among other things, fish and shellfish and is used as a seasoning in many Asian dishes.
In the goods declaration it must clearly state whether the product contains fish, shellfish or ingredients made from these. Fish oils are not a problem for most persons allergic to fish; however, some allergic individuals are so sensitive that they can react to trace amounts of protein found in these oils.


Persons with fish allergy often tolerate cod-liver oil as it is extremely well purified of proteins. As fish is an important source of omega 3 fatty acids, it is very important to take cod-liver oil or another omega 3 supplement if one has a fish allergy. Fish is also an important source of iodine and selenium. Iodine requirements can be covered by the use of milk products, but also fibrous corn products, offal, meat and in particular Brazil nuts are good sources of selenium.