The majority of those who are allergic to crustacean shellfish (shrimp, prawn, crab, lobster, crayfish) are allergic to the protein tropomysin which is found in all crustaceans.

Although it is possible to react to other proteins, no others have been identified. However, care should be taken as some ‘crab’ and ‘lobster’ on the market is actually fish - washed fish tissue made to look like the more expensive crab or lobster.

So those who are allergic to fish but not to crustaceans could be caught out. On the other hand those who are allergic to crustaceans would be OK - unless of course, a little shrimp, crab or lobster had been used as flavouring ... Ingredients listings should tell all - but often don’t.

Some people who are allergic to crustaceans will also be allergic to molluscs (clams, oysters, scallops, mussels, squid) which also contain the tropomysin protein - although cross reactions between crustacean and molluscan tropomysins do not always occur.

Courtesy of FAAN - www.foodallergy.org

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First published in March 2007

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