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The first two days after a colour or keratin service decide how much of the result you keep.
The 48-hour figure is borrowed from the safety side of the chair: a PPD patch test has to sit on the skin 48 hours before any colour, and a reaction can keep developing for up to 72 hours after it appears. The days around the appointment are when skin and scalp need watching, not just the hair.
The single biggest controllable risk is the shampoo. Washing with sulfates strips a smooth or keratin finish in about three washes at 12-15 °C water temperature. A finish rated to hold a blow-dry for 3-4 months can be gone inside a week if the wrong bottle is in the shower.
Colour fades unevenly by design. Roots on a previously lightened base take colour faster and fade sooner than virgin hair, so the first washes set the pattern for the whole 4-8 week cycle. Gentle washing from day one is what keeps the root line and the lengths ageing at the same speed.
On narrow screens, swipe or scroll the plate sideways.
Heat is part of the service itself: a keratin appointment ends with a 10-15 minute blow-dry that sets the finish. After that, the finish is maintained by what it is kept away from — sulfates chief among them — rather than by more heat.
Scalp awareness matters in this window too. Thirty-volume developer left on the scalp for over 40 minutes is the main cause of irritation burns, and a PPD reaction can build for up to 72 hours after it appears, so soreness or a spreading reaction in the days after a colour is information, not background noise.
For the intervals these first 48 hours are protecting, see How Often to Come Back for Root, Trim and Perm. For the appointment lengths themselves, see How Long Each Salon Service Takes.
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