Mollusc Allergy

Molluscs include mussels, clams, oysters, squid, scallops, octopus and snails. Allergy to molluscs is fairly common, can begin in childhood or adulthood, and is often lifelong.

Overview

Proteins in molluscs can trigger the immune system to react, releasing chemicals such as histamine. This causes allergy symptoms, which usually appear quickly after eating. Many people who react to one type of mollusc will react to others, due to the similarity of their proteins. Cross‑reactivity is common between shellfish such as crustaceans and molluscs, so some people avoid both categories entirely.

Symptoms

Mild to moderate symptoms may include:

• Itchy rash (hives)
• Tingling or itching in the mouth
• Swelling of lips, face or eyes
• Stomach pain or vomiting

Severe reaction (anaphylaxis) can include:

• Airway: throat or tongue swelling, difficulty swallowing
• Breathing: wheeze, shortness of breath, noisy breathing
• Circulation: dizziness, faintness, pale clammy skin, collapse

Who is at higher risk?

• Previous serious allergic reaction
• Asthma, especially if not well controlled
• Reactions to tiny amounts of mollusc

Treatment

Mild symptoms may be treated with oral antihistamines. If you are at risk of anaphylaxis, you should carry two prescribed adrenaline auto‑injectors (such as EpiPen® or Jext®) and know how to use them. In an emergency, call 999.

Avoiding molluscs

You will normally be advised to avoid all molluscs, cooked and raw, due to strong cross‑reactivity. This includes mussels, clams, oysters, squid, scallops, octopus and snails. Always check food labels: molluscs are one of the 14 major allergens in the UK, so must be clearly highlighted. Eating out carries a high risk of cross‑contamination, especially in seafood restaurants or buffets. Make staff aware of your allergy every time.

Important to know

• If you have symptoms after eating molluscs, see your GP.
• If prescribed adrenaline auto‑injectors, always carry two with you.
• Let restaurants and caterers know about your allergy clearly.
• Keep asthma well managed, as it can make reactions more severe.

Useful links

• NHS — Food allergy
• Allergy UK
• BSACI — Find an allergy clinic