Shellfish Allergy: Causes, Symptoms, and How to Stay Safe
Key Takeaways
- Shellfish allergy is one of Australia’s most common adult-onset food allergies.
- Crustacean allergies are typically more severe than mollusc allergies.
- Symptoms range from mild hives to life-threatening anaphylaxis.
- Avoidance and strict food label checking are essential.
- Always carry an EpiPen if diagnosed and use it immediately if severe symptoms occur.
- Cross-contamination is a major risk in kitchens, restaurants, and workplaces.
- Australian WHS laws require employers to provide safe environments for people with allergies.
- Shellfish allergy is usually lifelong, unlike some childhood food allergies.
- Early diagnosis, careful management, and prompt treatment save lives.
What Is a Shellfish Allergy?
A shellfish allergy occurs when the immune system overreacts to proteins in shellfish, wrongly identifying them as harmful. This response can trigger allergic reactions ranging from mild rashes to severe anaphylaxis.
Types of Shellfish
Crustaceans
- Prawns
- Crabs
- Lobsters
- Yabbies
- Moreton Bay bugs
These are the most allergenic group.
Molluscs
- Oysters
- Mussels
- Clams
- Scallops
- Squid
- Octopus
Molluscs are less commonly allergenic compared with crustaceans.
Prevalence in Australia
Shellfish allergy is one of the most common adult-onset food allergies in Australia. Around 2% of Australian adults are affected, with crustaceans being the leading cause of severe allergic reactions.
What Causes a Shellfish Allergy?
Immune System Response
Shellfish allergies are mainly caused by tropomyosin, a protein in shellfish. The immune system mistakes it for a threat, triggering the release of IgE antibodies and causing allergic symptoms.
Cross-Reactivity and Risk Factors
- People allergic to one crustacean (e.g. prawns) often react to others.
- Cross-reactivity between crustaceans and molluscs is less common.
- Risk factors include:
- Family history of allergies
- Adult-onset allergies often occur in the late 20s or 30s
- Occupational exposure, such as food handling or working in fish markets
- Family history of allergies
Shellfish Allergy Symptoms
Mild to Moderate Symptoms
- Hives or itchy skin rash
- Runny or blocked nose
- Stomach pain, nausea, vomiting, or diarrhoea
- Itchy mouth or throat
Severe Reactions (Anaphylaxis)
- Difficulty breathing or wheezing
- Swelling of the face, lips, tongue, or throat
- Dizziness or fainting
- Sudden drop in blood pressure
⚠️ Anaphylaxis is a medical emergency. Use an EpiPen immediately and call 000.
Diagnosing a Shellfish Allergy
Skin Prick Test
A small amount of allergen is introduced into the skin. A positive result produces redness and swelling.
Blood Testing (IgE Test)
Measures shellfish-specific IgE antibodies in the blood.
Oral Food Challenge
A controlled medical test where small amounts of shellfish are eaten under strict supervision to confirm the diagnosis.
Treating and Managing a Shellfish Allergy
Avoiding Shellfish
- Always check food labels
- Ask about ingredients when eating out
- Be cautious about cross-contact in shared kitchens
Epinephrine Auto-Injectors (EpiPen)
- Carry an EpiPen at all times if diagnosed
- Use immediately at the first signs of anaphylaxis
- Call 000 after administration
Antihistamines
Can relieve mild symptoms such as itching or hives, but they do not replace epinephrine.
Workplace Considerations & Legal Protections
Disclosing Allergies at Work
Inform employers or supervisors to ensure appropriate accommodations.
Food Handling and Cross-Contamination Risks
Workplaces that involve food must have strict protocols to prevent exposure.
Employee Protections under WHS
Australian Work Health and Safety (WHS) laws require employers to create safe workplaces, which includes allergy management strategies.
Cross-Contamination and Hidden Sources
Common Hidden Sources of Shellfish
- Fish and oyster sauces
- Asian cuisine dishes
- Soups and broths containing shellfish stock
- Fried foods cooked in shared oil
Food Labelling Laws in Australia
Packaged foods must include allergen labelling such as “Contains” or “May contain” statements. When in doubt, avoid the product.
Living with a Shellfish Allergy
Social Situations & Travel
- Inform restaurant staff
- Bring safe food to gatherings
- Research restaurants before travelling
Allergen Cards & Medical ID
Carry a wallet card or wear a medical bracelet listing your allergy.
Support Groups & Resources
- Allergy & Anaphylaxis Australia
- Local hospital allergy clinics
- Online communities for allergy support
Shellfish Allergy in Children vs Adults
Most cases develop in adulthood and are lifelong. In children, shellfish allergy is less common and rarely outgrown.
Outgrowing the Allergy: Is It Possible?
Unlike milk or egg allergies, shellfish allergy usually persists for life.
Latest Research and Treatments
Oral Immunotherapy and Experimental Treatments
While oral immunotherapy is being trialled for food allergies, it is not yet approved for shellfish due to safety concerns. Research is ongoing.
Frequently Asked Questions
What are the most common symptoms of a shellfish allergy?
Hives, swelling, stomach pain, breathing difficulties, and in severe cases, anaphylaxis.
Can you develop a shellfish allergy as an adult?
Yes. Many Australians experience adult-onset shellfish allergy, often in their 20s or 30s.
Is shellfish allergy the same as fish allergy?
No. Fish and shellfish contain different proteins, so it is possible to be allergic to one and not the other.
What should I do if I accidentally eat shellfish?
Use your EpiPen immediately if symptoms of anaphylaxis appear, and call 000.
Can shellfish allergy be cured?
No cure exists. Management relies on avoidance and emergency preparedness.
How do I protect myself from cross-contamination at work?
Disclose your allergy, follow workplace food safety protocols, and ensure an emergency plan is in place.
