Chemical ingredients used in dyeing and bleaching (such as ammonia and hydrogen peroxide) can destroy the scalp’s acidic protective barrier and directly damage hair follicle cells. In particular, bleaching contains high concentrations of hydrogen peroxide, causing strong scalp irritation, and damage accumulates with repeated procedures. If your scalp became sensitive and hair loss increased after treatment, a precision diagnosis to check for follicle damage is necessary. The earlier treatment begins during the recoverable stage, the better the results.