A good way to start a conversation about allergy alert tests with your customers is to ask them why they want to colour their hair, suggests Dr Meredith. “If the customer says it is because they are going out tonight then you really need to step in. They need to be told that the type of hair colourant they are buying requires an allergy alert test that needs to be done 48 hours in advance so they won’t be able to do that in time for this evening. But there might be alternatives available.â€