Allergic to crustaceans and shellfish

Food allergies result from a mistake in the body’s immune system that wrongly identifies certain foods as invaders. One of the most common food allergies is to shellfish. We can divide shellfish into two categories: crustaceans (shrimp, crab and lobster) and molluscs (oysters, squid, octopus, scallops and mussels). If a shellfish allergy is diagnosed, completely avoiding all types of shellfish is the best way to deal with it, although an allergy to shellfish does not necessarily mean that you will also have an allergic reaction to molluscs.

Symptoms of an allergy

The severity of the symptoms of an allergic reaction can range from mild to very severe. These symptoms can manifest themselves a few minutes after consuming shellfish but can sometimes last for hours. Here are some symptoms that indicate an allergic reaction:

  • Hives, itching or eczema
  • Swelling of the face, especially the lips, tongue and throat. This swelling can become quite serious or life-threatening.
  • Breathing difficulties
  • Wheezing or shortness of breath
  • Nausea or vomiting
  • Diarrhea
  • Stomach ache
  • Dizziness

In rare cases, an allergic reaction to shellfish can lead to life-threatening anaphylaxis. Anaphylaxis leads to severe breathing difficulties and should be treated as an emergency .

What causes the allergic reaction?

As with other food allergies, our body’s immune system is disrupted and identifies shellfish proteins as harmful invaders. Antibodies are activated with the aim of neutralizing proteins and histamine that have entered the body and play a major role in the symptoms we experience during an allergic reaction.
People who are allergic to shellfish should also be wary of products that also contain shellfish proteins. Some nutritional supplements contain crustacean shells and although studies have shown that it is quite unlikely that the allergic reaction is caused by crustacean shells, for people who are very sensitive to them, it is best to avoid ingesting glucosamine.
Another supplement that contains potential shellfish extracts are Omega-3 supplements. These are often made from fish, but it is still recommended to check the ingredients label before taking them.

Mollusk and oyster allergy

An allergy to oysters, unlike other forms of shellfish allergies, is much less common. The symptoms are similar to other food allergies and usually occur in mild, oral forms ranging from itching of the lips, throat and larynx to swelling of the lips, tongue, throat and palate. A common symptom of this form of allergy is also urticaria or nettle rash. In some cases, anaphylactic shock can also occur after consuming oysters.
Oysters are bivalve mollusks. If a person is allergic to a particular bivalve mollusk such as clams , mussels and scallops, there is a good chance that person will also need to avoid other mollusks. This also applies to snails, squid, octopus and squid. The allergic symptoms after eating oysters usually manifest within ninety minutes, but this can sometimes take longer.


There is already a law that states that all packaged foods containing shellfish must specifically state on the label which shellfish they are. It is possible that a particular product used to contain shellfish extracts and no longer does. So always check the label before consuming the product.

Shellfish to avoid:

  • barnacle
  • crab
  • crayfish
  • krill or shrimp-like species
  • lobster
  • shrimps
  • scampi

According to the FASFC, molluscs are not considered important genes and therefore do not need to be specifically mentioned on the label. It is important to consciously pay attention to the following molluscs:

  • abalone
  • clams
  • calamari
  • sea snail
  • Mussels
  • octopus
  • oysters
  • sea cucumber
  • sea urchin
  • scallops
  • snails
  • whelk



Research has shown that heredity plays an important role in a shellfish allergy. If your parents suffer from this allergy, there is a good chance that you are also allergic. To prevent you from ever having an allergic reaction to shellfish, it is advisable to have it tested by your doctor.
A blood or skin test at your GP is the most effective way to know the exact extent of your shellfish allergy. During the skin test, small pricks are given in the skin after which it is exposed to a small amount of shellfish protein. The intensity of the reaction is judged by the bumps that appear on the skin.

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  • Food allergies