The pre-service inspection: what a good beautician checks before opening the kit
Watch what happens in the first ten minutes, because that is the diagnostic phase, and skipping it is the clearest early warning you will get. For colour, the professional standard is a patch test of the actual developer and dye behind the ear or on the inner arm 48 hours before application. PPD allergy reactions range from an itchy hairline to facial swelling that needs emergency care, and prior tolerance is not a guarantee, because sensitisation builds with exposure. Any vendor willing to apply permanent colour to a new client with no patch test and no questions asked is telling you how they handle every other safety step.
For hair work generally, the checks are quick but specific: a porosity check, wetting a strand to see how fast it absorbs, which decides processing time; a look at the scalp for irritation, psoriasis or folliculitis, which are reasons to pause and, for anything persistent or painful, reasons to see a DHA- or DoH-licensed dermatologist rather than a beautician; and a history question about henna. Henna matters because conventional dye and lightener over henna-treated hair can react unpredictably, and a lot of hair in this market has henna in its history even when the client has forgotten.