Table of Contents

Shellfish Allergy: Symptoms, Causes & Treatment in Australia

Key Takeaways

Shellfish allergy is usually lifelong and distinct from fish allergies.
Crustaceans (prawns, crabs, lobsters) are the most common triggers.
Symptoms may appear within minutes and range from mild hives to severe anaphylaxis.
Anaphylaxis requires urgent EpiPen use and calling 000 in Australia.
Diagnosis is done through skin prick tests, blood tests, or food challenges under medical supervision.
Workplace safety and strict food labelling checks are essential for prevention.

What Is a Shellfish Allergy?

A shellfish allergy is a hypersensitive immune response to proteins found in certain marine animals. Unlike shellfish intolerance, an allergy triggers the immune system, leading to symptoms ranging from mild discomfort to life-threatening reactions. Shellfish allergies are usually lifelong, unlike other food allergies, such as milk or peanut allergies.

It’s important to note that a shellfish allergy is distinct from a fish allergy. People who are allergic to shellfish can often safely eat finned fish without issue.

Causes and Risk Factors

While the exact cause of shellfish allergies is unclear, there are several factors that increase the risk:

Family History: A genetic predisposition to allergies can increase the likelihood of developing a shellfish allergy.
Adult-Onset: Shellfish allergies can develop later in life, even if you have eaten shellfish without issues before.
Occupational Exposure: People who work in the seafood industry or in environments where shellfish are handled may be at higher risk.

Types of Shellfish That Cause Allergies

Shellfish fall into two main categories:

Crustaceans: prawns, crabs, lobsters. These are the most common triggers of allergic reactions in Australia.
Molluscs: squid, mussels, oysters, scallops. Reactions to molluscs are less common but can still be severe.

How the Immune System Reacts to Shellfish Allergens

In a shellfish allergy, the immune system mistakenly identifies shellfish proteins as harmful invaders. This triggers the production of antibodies and the release of chemicals like histamine, leading to symptoms such as itching, swelling, and in severe cases, anaphylaxis.

Shellfish Allergy vs. Intolerance

A shellfish allergy is an immune system response, while shellfish intolerance refers to a digestive issue that does not involve the immune system. Intolerance to shellfish can cause discomfort, such as stomach pain or bloating, but it is not life-threatening like an allergy.

Common Shellfish Allergy Symptoms

Shellfish allergy symptoms vary in severity and can affect multiple body systems. Symptoms typically occur within minutes to an hour after exposure.

Skin Symptoms

Hives (raised, red, itchy welts)
Eczema flare-ups
Swelling of lips, face, or eyelids
General redness or itching, especially around the mouth

Digestive Symptoms

Nausea
Vomiting
Abdominal pain
Diarrhoea

These symptoms usually begin within 30–60 minutes of ingesting shellfish.

Respiratory Symptoms

Sneezing
Wheezing
Coughing
Nasal congestion
Throat tightness
Shortness of breath

Cardiovascular and Neurological Symptoms

Dizziness or light-headedness
Fainting
Weak pulse
Confusion or anxiety

These may indicate a severe reaction requiring urgent attention.

Recognising Severe Allergic Reactions (Anaphylaxis)

Anaphylaxis is a life-threatening medical emergency requiring immediate action. If you suspect anaphylaxis, use an EpiPen and call 000 for emergency medical assistance.

Anaphylaxis Symptoms

Swelling of the tongue or throat
Difficulty breathing
Sudden drop in blood pressure
Rapid, weak pulse
Loss of consciousness

Emergency Response and Use of EpiPen

If anaphylaxis is suspected:

Use an adrenaline auto-injector (EpiPen) immediately.
Call 000 for emergency help.
Lie the person flat and elevate their legs, unless this makes breathing harder.
Stay with the person until help arrives.

When Do Symptoms Start and How Long Do They Last?

Immediate-Onset Reactions

Most reactions begin within minutes of eating shellfish or coming into contact with shellfish residue.

Delayed-Onset or Biphasic Reactions

In some cases, symptoms can return hours later (biphasic reaction). Medical observation for at least 4–6 hours after initial treatment is recommended.

Shellfish Allergy Testing & Diagnosis in Australia

If you suspect a shellfish allergy, consult a GP who can refer you to an allergist or immunologist under Medicare.

Allergy Testing Options

Skin prick tests
Blood tests (specific IgE)
Supervised food challenges (in specialist settings)

Workplace and Lifestyle Implications

Shellfish allergies require careful management in workplaces, especially in hospitality, food service, and shared kitchen environments.

Preventing Exposure at Work or Social Events

Check ingredients in catered food or shared meals.
Be cautious in environments involving food handling.
Avoid cross-contact in shared cooking appliances.

Disclosing Allergies and Managing Safety

Notify employers, HR, and colleagues about your allergy. In high-risk settings like hospitality, formal allergy management plans may be needed.

Travel and Dining Out Tips

Dining Out: Always ask about the ingredients in dishes, especially in seafood-heavy cuisines like Asian or Mediterranean.
Travel: Carry a medical letter explaining your allergy in case you need to visit a doctor abroad. Also, research food allergies in the country you are visiting, as labelling practices vary worldwide.