Clam allergy
Mollusc allergy to clams.
About clam allergy
Clams are molluscs, the shellfish group that also includes mussels, oysters, scallops, squid and snails. Molluscs are a named allergen on UK food labels, and allergy to them is an IgE-mediated allergy that often persists into adult life. The immune system reacts to muscle proteins, particularly one called tropomyosin, and exposure triggers a rapid release of histamine and other chemicals that cause the reaction.
Shellfish allergy, including clam, is well known for causing severe reactions. Symptoms usually begin within minutes of eating and can range from an itchy mouth, hives and swelling to vomiting, wheezing and, at the severe end, anaphylaxis with breathing difficulty or collapse. Because tropomyosin is shared across shellfish, people allergic to clam may cross-react with other molluscs and sometimes with crustaceans such as prawns, crab and lobster; there is also a recognised link with house-dust-mite allergy, as dust mites contain a similar protein. Cooking vapours from shellfish can trigger symptoms in some highly sensitive people.
Diagnosis is made by an allergy specialist using skin-prick or specific-IgE blood tests, sometimes with a supervised food challenge. Management means strict avoidance of clams and, depending on testing, other molluscs and shellfish, plus careful attention to seafood dishes, sauces and cross-contamination. People at risk of severe reactions are prescribed an adrenaline auto-injector. A severe reaction is a medical emergency: use adrenaline and call 999 immediately.
Common triggers
- Clam and products containing it
Symptoms
- Itching or tingling in the mouth
- Hives, itching or eczema
- Swelling of the lips, face, tongue or throat
- Stomach cramps, nausea, vomiting or diarrhoea
- Wheezing or trouble breathing
- In severe cases, anaphylaxis
Avoidance & management
- Read ingredient labels every time
- Ask about ingredients and cross-contamination when eating out
- Keep the food out of shared cooking areas
- Carry prescribed antihistamines or an adrenaline auto-injector
- Seek emergency help for any severe reaction
Sources & references
Allergy safety: what everyone should know
Mild-to-moderate reaction signs
- Itching, hives or a raised rash
- Swelling of lips, face or eyes
- Tingling mouth, sneezing, runny nose
- Stomach pain, nausea or vomiting
Anaphylaxis — call 999 (UK) or 112 (EU) immediately
- Difficult or noisy breathing, wheeze, persistent cough
- Swelling of the tongue or tightness in the throat
- Dizziness, collapse, pale and floppy (young children)
- Use an adrenaline auto-injector (e.g. EpiPen) at once if prescribed, then call an ambulance even if symptoms improve
Allergy or intolerance? A true allergy involves the immune system and can escalate quickly; an intolerance (e.g. lactose intolerance) is unpleasant but not life-threatening. The symptoms overlap, so self-diagnosis is unreliable.
Getting tested: home-testing kits based on IgG are not diagnostically valid. If you suspect an allergy, ask a GP for referral to an allergy clinic for skin-prick or specific-IgE testing and a supervised food challenge where appropriate.