Around 0.1 per cent of the European population demonstrates an allergic reaction to crustaceans and/or to molluscs in provocation tests. There is a higher prevalence of allergies in countries where a lot of seafood is consumed. Allergies to crustaceans and molluscs are among the most common food allergies in Scandinavia, Portugal and Spain.
The main allergens in crustaceans and molluscs are called tropomyosins. These proteins are essential for muscle movement. They are not destroyed by heat, which means that both raw and cooked crustaceans and molluscs can provoke allergies.
While an allergic reaction is usually triggered when crustaceans or molluscs are eaten, very sensitive people can develop allergy symptoms just by breathing in the steam from cooked seafood. Skin contact can also provoke allergic reactions. Fishery and food service workers are particularly vulnerable to this form of sensitisation.
People can have allergic reactions to individual crustacean species or to several different ones. This is also the case for mollusc species. Still others are allergic to both crustaceans and molluscs, and cannot tolerate any kind of seafood.
Incidentally, some people who are allergic to house dust mites also develop an allergy to crustaceans and molluscs. This is because house dust mites, like crabs, belong to the phylum of arthropods and have tropomyosins. In individuals who are already sensitised to house dust mite tropomyosins, the proteins of the crustaceans and molluscs, which are similar in structure, are considered dangerous by the immune system. The food allergy then develops in addition to the house dust mite allergy. Sometimes the order is reversed, and a house dust mite allergy develops after the crustacean or mollusc allergy.
Crustacean and mollusc allergies 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 may occur. Skin reactions may also occur, including redness, itchiness or hives. In some cases, the airways are affected and allergic rhinitis or asthma symptoms can develop.
Shellfish Allergy in Childhood
Allergies to crustaceans and molluscs can appear as early as in infancy. It is estimated that 0.1 per cent of all children in Europe are allergic. While food allergies to milk or eggs often subside over time, studies suggest that crustacean and mollusc allergies generally remain for life.
As a first step in diagnosing a crustacean and/or mollusc 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 crustacean or mollusc protein under medical supervision. The results confirm whether they trigger an allergic reaction or whether they can be removed from the list of suspected allergens.
The symptoms of a crustacean and mollusc allergy must be distinguished from other symptoms that mimic an allergy, but which are instead triggered by bacteria, viruses or toxins in the shellfish. For example, microalgae in mussels can produce toxins that trigger a reaction similar to an allergy
The best way to reduce the symptoms of a crustacean and mollusc allergy is to avoid the triggers. An allergist can decide which specific types of seafood need to be excluded from the diet after carrying out a thorough diagnostic procedure.
People who are highly allergic to crustaceans and/or molluscs and at risk of anaphylactic shock from exposure to even the smallest amounts of 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