Table of Contents

Different Types of Shellfish Allergies Explained

Key Takeaways

Shellfish allergies are immune reactions, not food intolerances, and can be severe.
There are two main types: crustacean allergies (prawns, crabs, lobsters) and mollusc allergies (mussels, oysters, squid).
Crustacean allergies are more common and more likely to cause anaphylaxis.
Symptoms range from itching and hives to life-threatening breathing difficulties.
Diagnosis in Australia usually involves a GP referral, skin prick tests, or IgE blood tests.
Management includes strict avoidance, label checking, cross-contamination prevention, and emergency preparedness.
Always carry an EpiPen if prescribed and have an allergy action plan.
With the right precautions, you can still enjoy dining out, socialising, and work safely.

What Is a Shellfish Allergy?

A shellfish allergy happens when your immune system mistakenly treats proteins in shellfish as harmful. This triggers an allergic reaction, which can be serious even in tiny amounts. Unlike food intolerances that mainly affect digestion, a shellfish allergy involves the immune system and may lead to life-threatening anaphylaxis.

Crustaceans vs Molluscs

Shellfish are divided into two main groups:

Crustaceans: prawns, crabs, lobsters, yabbies, Moreton Bay bugs
Molluscs: mussels, clams, oysters, scallops, squid, octopus

Crustacean allergies are more common in Australia and are more likely to cause severe reactions than mollusc allergies.

Types of Shellfish Allergies

Crustacean Allergy

This is the most widespread shellfish allergy in Australia. Reactions often occur with prawns, crabs, and lobsters.

Common symptoms include:

Itching or tingling in the mouth
Hives or skin rash
Swelling of the lips, face, or throat
Breathing difficulties
Nausea or vomiting
Anaphylaxis

The main trigger is tropomyosin, a protein that remains allergenic even after cooking.

Mollusc Allergy

Mollusc allergies are less common but can still be serious. Examples include oysters, scallops, mussels, clams, and squid.

Symptoms can range from mild skin reactions to more severe responses, although anaphylaxis is reported less often than with crustaceans. Some people allergic to molluscs can still eat crustaceans, but cross-reactions are possible.

Cross-Reactivity Between Shellfish

Cross-reactivity occurs when your immune system reacts to similar proteins in both crustaceans and molluscs. Some people are allergic to only one group, while others react to both. Allergy testing, such as blood tests for specific IgE, helps identify which types are problematic for you.

Symptoms of Shellfish Allergy

Reactions can appear within minutes to two hours of eating or handling shellfish.

Common Symptoms

Tingling or itching in the mouth
Hives or skin rash
Abdominal cramps
Diarrhoea or vomiting

Severe Symptoms

Swelling of the lips, face, or throat
Breathing difficulties or wheezing
Dizziness or fainting
Drop in blood pressure (anaphylaxis)

If you notice signs of a severe reaction, seek emergency medical attention immediately.

Diagnosis and Testing

In Australia, diagnosis usually begins with a GP, who may refer you to an allergist.

Skin Prick Test

A small amount of shellfish extract is applied to your skin with a tiny needle. A raised bump indicates a possible allergy.

Blood Test (Specific IgE)

This measures IgE antibodies in your blood that react to shellfish proteins. It helps confirm sensitisation.

Oral Food Challenge

Because of the risk of anaphylaxis, this test is rarely used for shellfish allergies. If performed, it is only done in a hospital with emergency care available.

Managing Shellfish Allergies in Daily Life

Reading Food Labels in Australia

Food Standards Australia New Zealand (FSANZ) requires crustacea and molluscs to be clearly labelled. Still, you should be cautious with:

Processed foods
“May contain” statements
Imported products with unclear labelling

Avoiding Cross-Contamination

To reduce risk at home, work, or restaurants:

Use separate utensils and cookware
Clean surfaces thoroughly
Avoid buffets and shared platters
Clearly inform food staff of your allergy

For those in hospitality or food services, proper training is essential for safety and compliance.

Emergency Preparedness

Carry an EpiPen if prescribed
Have an allergy action plan from your doctor
Inform friends, family, and coworkers
Wear a medical alert bracelet if possible

Treatment Options

Antihistamines for Mild Reactions

These may ease minor symptoms such as hives or itching but are not suitable for severe reactions.

Epinephrine for Severe Reactions

Adrenaline (epinephrine) is the first-line treatment for anaphylaxis and must be administered immediately. Training in EpiPen use is essential for you and those around you.