Sharon

You don’t. Just occasionally when one investigates a situation it is clear that it is an allergy, but even then one has to test to ensure this is correct – and of course test with the relevant chemical. (If you don’t test with the relevant chemical you can easily end up with what we call a ‘clinically accurate, occupationally irrelevant’ diagnosis!) Furthermore, an irritant contact dermatitis is seldom to a single chemical but more usually to repeated skin contact with a whole raft of different irritants.

Chris