Do a patch test, every single time
The allergen in permanent hair colour is paraphenylenediamine, or PPD. It is present in almost every box and salon colour that promises full grey coverage, and it is the reason some women end up with a swollen scalp, weeping skin, or a trip to the emergency room after a routine appointment. The Contact Dermatitis Society of India has flagged PPD sensitivity as one of the most underreported cosmetic reactions in the country, partly because women assume that tolerating a colour once means they can tolerate it forever. They cannot. Sensitisation builds over repeated exposures. A patch test done 48 hours before your appointment, a small amount of the mixed colour applied behind the ear or inside the elbow, is the only reliable screen. Most salons skip it because it adds a day to the booking cycle. Do it yourself at home before you go in.
