What is considered a shellfish allergy?

Here are some of the most frequently asked questions around shellfish allergies:

• Can you be allergic to shellfish?
• What is the most common shellfish allergy?
• What are the symptoms of a shellfish allergy?
• What are considered shellfish?
• Is a shellfish allergy the same as a Crustacean allergy?
• Which foods should you avoid if you are allergic to shellfish?
• Does a shellfish allergy include Molluscs?
• What are the drugs to avoid with a shellfish allergy?

Now let’s find out the answers...

Can you be allergic to shellfish?

Yes, you can be allergic to shellfish - in fact, both types of shellfish, Crustaceans and Molluscs, are among the 14 major food allergens.

This means Caterers and food businesses are required by law to be able to provide customers with accurate information about whether they are included in any of the food products they produce, sell or serve.

What are considered shellfish?

Basically speaking, shellfish are an invertebrate animal defined by living in water (usually saltwater but sometimes freshwater) and having a shell. You can get 2 main types of animals that are considered shellfish - Crustaceans and Molluscs.

Crustaceans are invertebrates that have an exoskeleton and a segmented body, and include lobsters, crabs, crayfish and prawns.

Molluscs, of which there are over 85,000 species, have a shell and a soft body and include clams, mussels, oysters, scallops and squid.

What is the most common shellfish allergy?

Crustaceans and Molluscs are both among the 14 major food allergens, which means allergies to them are among the most common.

It is difficult to say whether more people have Crustacean or Mollusc allergies, though allergies to crab, lobster mussels return the most searches on Google, and shrimp allergies are throught to be among the most studied.

Can you be allergic to Molluscs but not Crustaceans?

Yes you can be allergic to Molluscs but not Crustaceans, and you can be allergic to Crustaceans but not Mollusics - as they are considered separate allergens and not lumped together within the 14 major food allergens.

Crustaceans are arthropods - invertebrates that have an exoskeleton and a segmented body, Molluscs are also invertebrates, but with a soft body, and many have a hard, protective shell. They are different species, but biologically similar enough that those with an allergy to one may experience cross-reactivity with the other - if not an allergic reaction. This means potentially milder symptoms, such as redness or itchiness in the skin.

What are the symptoms of a shellfish allergy?

The symptoms of a shellfish allergy, like other allergies, generally appear within an hour or consuming or coming into contact with the shellfish the person is allergic to - usually of either the Crustacean variety or Mollusc variety, but sometimes both.

These symptoms include a red, itchy rash, dizziness, vomiting, nausea, a sore or tingling mouth, wheezing, shortness of breath, diarrhoea, swelling of the face and/or throat (including having difficulty swallowing) and abdominal pain.

Crucially, an allergic reaction may also involve anaphylaxis - which can be fatal if not treated as soon as possible. If anaphylaxis does occur, an ambulance must be called for immediately, and the symptoms of anaphylaxis include difficulty breathing, dizziness, faintness, a swollen tongue and difficulty speaking or swallowing, a tight chest and collapsing and losing consciousness.

Is a shellfish allergy the same as a Crustacean allergy?

A shellfish allergy is not exactly the same as Crustacean allergy - as Crustaceans are only one type of shellfish. A person with a shellfish allergy would technically not be able to eat Crustaceans or Molluscs, whereas a person with s Crustacean allergy may be able to eat Molluscs without triggering a reaction. It is important for a person with a Crustacean allergy to know what shellfish are considered Crustaceans. You can find out more about a Crustacean allergy in our Deep Dive here.

Which foods should you avoid if you are allergic to shellfish?

If you are allergic to all shellfish, you should avoid foods that contain or have been cross-contaminated with both Crustaceans and Molluscs.

Crustaceans include amphipods, barnacles, crabs, crayfish, isopods, lobsters, prawns, scampi, sea spiders, shrimp (Including mantish and mussel shrimp). Molluscs include octopus, oysters, cuttlefish, snails, squid, scallops, mussels, clams, and cockles.

People with a shellfish allergy should check ingredients labels carefully to make sure that none of the above or their derivatives are included - they will be highlighted, e.g in bold type or capital letters.

Our 14 allergens page lists some of the surprising foods you can find allergen ingredients in.

Does a shellfish allergy include Molluscs?

Yes, Molluscs like squid, scallops and oysters are a type of shellfish and therefore included in a shellfish allergy.

What are the drugs to avoid with a shellfish allergy?

Some people with a shellfish allergy have to be careful around certain weight loss drugs/supplements as they are made with chitin, a chemical compound found in shellfish shells. It is always best to check with a doctor before consuming such drugs or supplements - even though people allergic to lobsters (for example), may be allergic to proteins in the animal’s meat rather than the shell. There are also some calcium supplements that contain oysters (the shell not the meat), and cartilage and joint health glucosamine supplements that similarly contain lobster or crab shell.