Customers need to know that an allergy alert test has to be carried out 48 hours before every hair colouring, even if they’ve used the same hair colouring product before, says Dr Emma Meredith, head of scientific and technical services at the Cosmetic, Toiletry and Perfumery Association (CTPA). “What people don’t always realise is that an allergy can build up over time,” she says.

 

Dr Meredith uses the analogy of a glass of water overflowing to explain how an allergy can develop: an empty glass can be filled with a drop of water again and again, but one day the glass could get so full that it spills over the top. This is the body reaching the point where it says, “I really am allergic to this hair dye and I’m going to react this time.”

Each time a customer dyes their hair, they may notice a little bit of redness, so it’s important to look out for signals that show their allergy level is starting to build up.

Follow pack instructions

Customers should read and follow all of the instructions on product packs as well as in the information leaflets carefully and closely as each manufacturer may have slightly different steps that need to be followed. The general idea is to place a small amount of hair colourant on a discreet skin site, such as in the crook of the elbow or behind the ear, two days before colouring their hair.

It needs to be done so far in advance because we are constrained by the biology of our bodies and 48 hours is how long it takes for an allergic reaction to develop within the body. A customer will know if they’ve had a reaction because they will experience stinging, burning, a rash, swelling, redness or maybe even some blistering.