However, fish is one of the foods that most commonly trigger a food allergy. Around 0.1 per cent of the European population demonstrate a reaction when exposed to fish in provocation tests. The numbers vary by country. In regions such as Scandinavia, where a lot of fish is consumed and processed, fish allergies are more common than in Germany.
Allergic reactions to fish are mainly caused by a specific kind of protein called parvalbumin. The white muscle tissue of fish is especially high in parvalbumins – much higher than in red muscle tissues. This explains why fish species such as tuna, which have mostly red muscle` tissue, are often better tolerated by people who are allergic to fish.
Parvalbumins are relatively heat stable. This means that they are not destroyed through cooking or grilling. Both raw and cooked fish can therefore trigger allergy symptoms. Most people with fish allergies react to several fish species. Monoallergies – allergies to individual fish species – also exist.
While an allergic reaction is usually triggered when fish is eaten, very sensitive people develop allergy symptoms just by breathing in the steam from cooked fish. An allergy can also be caused by inhaling dust containing dried fish particles or through skin contact with fish, for example, during fish processing.
But a fish allergy does not necessarily mean that seafood, such as mussels or prawns, will also provoke an allergic reaction. Surimi, or imitation crabmeat, must be approached with caution. It is a common ingredient in seafood ready meals and is made from fish that has been chopped up and pressed into a mould.
A fish allergy can cause mild or severe reactions in various organs. Symptoms range from what is called oral allergy syndrome, in which the mucosa in the mouth and throat start to tingle or swell a few minutes to hours after exposure, to anaphylactic shock accompanied by difficulty breathing and circulatory collapse.
Abdominal pain, vomiting or diarrhoea can occur. The skin may also develop allergic reactions. Apart from itchiness, redness and hives, a fish allergy can also trigger or worsen an eczema flare-up. In still other cases, the airways can be affected, with reactions ranging from allergic rhinitis to asthma symptoms.
Fish Allergy in Childhood
Fish allergies can appear as early as in infancy. It is assumed that less than 0.1 per cent of all children in Europe are allergic to fish. While food allergies to milk or eggs often subside over time, studies suggest that fish allergies generally remain for life.
As a first step in diagnosing a fish allergy, the doctor asks the patient about his or her eating habits and symptoms.
If an allergy is suspected, skin and/or blood tests are conducted in order to confirm it. These tests reveal an allergic disposition to certain substances but do not provide evidence of an actual allergy. For this reason, an additional diagnostic procedure, the provocation test, is conducted to rule out any doubts. For this test, the patient eliminates the allergen from the diet for a certain period. He or she is then given small amounts of fish protein under medical supervision. The results confirm whether fish triggers an allergic reaction or whether it can be removed from the list of suspected allergens.
The symptoms of a fish allergy must be distinguished from other symptoms that are similar but are instead triggered by a specific kind of fish poisoning. Certain fish species such as mackerel, tuna or herring harbour bacteria that produce substantial amounts of histamine when the fish have been improperly refrigerated and stored for a longer period of time. This histamine is not destroyed when heated and can provoke symptoms that mimic an allergy, such as nausea and vomiting, skin redness, and difficulty breathing. These kinds of symptoms can also be caused by certain bacteria, viruses or venoms in fish.
The best way to reduce the symptoms of a fish allergy is to avoid the triggers. An allergist can decide whether all fish species or only certain individual fish species need to be excluded from the diet after carrying out a thorough diagnostic procedure.
People who are highly allergic to fish and at risk of anaphylactic shock from exposure to even the smallest amounts of fish protein must carry an emergency kit with them containing an adrenaline auto-injector, a corticosteroid (in liquid or tablet form) and an antihistamine (in liquid or tablet form).
Prof. Dr. med. Dr. h.c. T. Zuberbier
Last changes made: July 2016