A patch test is only required when hair dye comes into contact with the scalp. However it is still important to do a patch test for other colour treatments such as hair highlights where foils are used, as the foils can leak and come into contact with the skin.

Is patch testing a legal requirement?

If you're a hairdresser, patch testing for hair dye is a legal requirement under Section 3 of the Health and Safety at Work Act. If you're a beauty therapist, you also need to patch test your clients before certain treatments.

Can you be allergic to highlights?

When someone has an allergy to hair dye, they are most likely allergic to one of the chemicals in the dye rather than the entire product. The most common cause of these allergic reactions is para-phenylenediamine, also called PPD.