Fish allergy: symptoms, diagnosis and treatment

Fish is a valuable product for a healthy diet. Not only does it contain a lot of protein, fatty fish is also healthy because of the so-called good fats (with so-called polyunsaturated fatty acids) that fit in a cholesterol-lowering diet and fish contains many vitamins and other important nutritional components (vitamin A, vitamin D, various B vitamins , iodine, fluorine, selenium and phosphorus). Unfortunately, fish is sometimes also the cause of health problems due to a food allergy. The protein in the fish that causes the allergy does not disappear through heating, so cooking or baking fish cannot prevent the allergy. About 0.1 to 0.2% of people have a fish allergy, among them children and adults. It is an allergy that usually cannot be overcome.

What causes a fish allergy?

Fish contains a protein called parvalbumin. This protein is the culprit in almost all cases of fish allergy. We call such a culprit an allergen: a component of a substance that can cause allergic reactions. The allergens are the same for freshwater and saltwater fish. Sometimes people with a fish allergy can eat fish with predominantly red meat such as swordfish or tuna. Relatively little parvalbumin is present in these fish. However, caution is advised. This is because this is a very powerful allergen. Highly sensitive people also react to dust from dried fish, cooking fumes from fish preparation, or minimal fish scraps that end up on utensils or other foods during preparation.

Fish allergy occurs in both children and adults. The frequency depends on where you live. In countries where fish is an important part of the local diet, fish allergy is logically also more common. It is an allergy that one does not grow over, as with some other allergies and that one is therefore attached to for life.

Who is allergic to fish often reacts to several fish species, but it is not necessary that one is also allergic to shellfish (shrimps, mussels, lobster and crab), squid or caviar. However, it is often the case that people who are allergic to fish are also allergic to other seafood. There are so-called cross reactions: reactions of the body's defense against a foreign substance that resembles another foreign substance. It is therefore often recommended not to take any risks and to avoid eating all types of fish and seafood.

Because a fish allergy is considered dangerous - it can be killed quite quickly if not adequately addressed - it is important to diagnose it in time. Hence, it is important to know the symptoms. These can occur when exposed to very small amounts of fish.

The first symptoms of fish allergy are tingling in the oral cavity or palate, rash, watery eyes, a runny nose and wheezing. Sometimes the first symptoms are not so severe. Then one often sees complaints of the digestive system such as vomiting and diarrhea. In the worst case, an allergic reaction to fish can lead to anaphylaxis, a potentially life-threatening reaction that causes difficulty in breathing and can shock the body and cause death.

During the medical history (the patient's personal story), the doctor will look at the symptoms and perform a physical examination if necessary. Depending on this, he can perform a blood test and possibly a skin prick test. A positive skin prick test or the presence of the fish protein specific gE antibody in the blood is an indication of fish allergy. However, in order to determine with certainty that fish allergy is present, strict, well-defined protocols must be carried out by an allergist (an expert in the field of allergies), because of the danger of exposure to the allergen during the study. Confirming the diagnosis of fish allergy occurs when the symptoms disappear after elimination (omission of certain substances) and reappear on reintroduction (re-addition of the substance) or when a so-called double-blind placebo-controlled food challenge leads to a positive result. In such an examination, neither the patient nor the physician knows which meals used in the challenge contain fish and which are not. It is therefore not known which food contains the allergen and which food contains a placebo (fake substance). This is a scientific way of making a diagnosis. In this way it is also possible to investigate at what quantities the patient reacts and whether this has possibly (although rare) outgrown the allergy.

Confusion sometimes arises between histamine poisoning from fish and fish allergy, as the symptoms are similar. However, there are several causes. If fish is not fresh, it can contain a lot of histamine. This is a substance that is developed during an allergic reaction. However, there is no fish allergy in this case. Canned fish, in particular, can be high in histamine.

Because of the very serious consequences that a fish allergy can have, it is important to know how to deal with this.

First of all, it is important to avoid fish and fish products. That is why it is important to know which foods may contain fish and to read labels and packaging carefully. Based on the EU Food Information Directive (EU Regulation No. 1169/2011) and a list of the Codex Alimentarius Commission (an international forum / organization of the UN in which 189 countries and one organization - the European Union - participate with aim to develop international standards for food products in order to protect international public health and promote fairness in trade in food products), each ingredient derived from fish should be listed on the label. If you are going to eat in a restaurant, it is important to inform the staff that you are allergic to fish. It is important to check whether kitchen utensils or cooking oil have come into contact with fish.

Anaphylaxis requires an injection of epinephrine (adrenaline). If someone, especially someone known to be allergic to fish, shows the symptoms of an allergic reaction after eating fish, an adrenaline syringe and other antihistamines will be administered immediately. It is wise to inform those around them about the allergy. In case of exposure, go immediately to the nearest hospital because of the risk of anaphylactic shock.