Shellfish Allergy
Also known as: Crustacean allergy, Seafood allergy
Shellfish allergy is one of the most common adult-onset food allergies and among the most persistent — it rarely resolves with age. Crustaceans (shrimp, crab, lobster) and molluscs (oyster, squid, clam) can each trigger reactions.
Category
Food Allergies
Severity
Can be Life-ThreateningPrevalence
One of the top three adult food allergies globally; affects 1–2% of adults.
Emergency Information
Use prescribed adrenaline for throat swelling or severe breathing difficulty; call emergency services immediately.
Symptoms
Airways & Breathing
- Throat swelling
- Wheezing
- Shortness of breath
Skin
- Hives
- Angioedema (facial swelling)
- Widespread itching
Digestive
- Nausea
- Vomiting
- Diarrhoea
- Abdominal cramps
Systemic / Other
- Anaphylaxis
- Dizziness
- Drop in blood pressure
How It's Diagnosed
- Skin prick test to shrimp, crab, lobster, and/or oyster extracts
- Specific IgE to tropomyosin (the primary shellfish allergen, cross-reactive between crustaceans)
- Supervised oral food challenge when clinical history and test results conflict
Avoidance Strategies
- Distinguish crustacean from mollusc allergy — you may tolerate one but not the other
- Steam from cooking shellfish can trigger reactions in highly sensitive individuals
- Watch for shellfish in sauces, stocks, soups (bouillabaisse, tom yum), and paellas
- Glucosamine supplements are sometimes derived from shrimp shells — check the source
- Inform restaurant staff, especially in seafood-centric cuisines
Cross-Reactivity
- Tropomyosin is shared between crustaceans and house dust mites — rare cross-reactivity possible
- Crustacean and mollusc tropomyosins differ enough that many crustacean-allergic patients tolerate molluscs
Crustaceans vs molluscs
Shellfish allergy is not one allergy — it encompasses two distinct animal classes. Crustaceans (shrimp, crab, lobster, crayfish, prawn) and molluscs (oyster, clam, mussel, scallop, squid, octopus) contain different proteins. Many people are allergic to crustaceans but not molluscs, and vice versa.
Your allergist can test for each group separately to clarify what you need to avoid.
Hidden shellfish sources
- Worcestershire sauce (traditionally contains anchovies — a fish, but check)
- Caesar dressing (anchovies)
- Bouillabaisse, bisques, and seafood stocks
- Sushi, sashimi, and Asian seafood dishes
- Some dietary supplements (glucosamine from shrimp shells)
Medical disclaimer
This page is for educational purposes only. Allergy diagnosis and management must be carried out by a qualified allergist. Do not attempt to test yourself with suspected allergens. Always carry prescribed emergency medications and follow your written action plan.
Reviewed 2026-06-01 · Looms Medical Team