In chemical peeling of the skin for photoaging, the absorption of trichloroactic acid (TCA) after contact with the epidermis depends on the photoaged status of the skin in concert with the actual method of application. Protein coagulation and increasing penetration are reflected in the frost, but only an approximate inexact definition of depth estimation can be ascertained from the color. Although 35% TCA has an excellent record of safety and clinical results, 50% TCA is frought with more complications owing to the inherent unpredictability of the agent, and the addition of additives to slow penetration does not alter its increased capability for scarring. Either 35% TCA as a single agent or techniques to admit 35% TCA to deeper depths in the dermis by altering the epidermis immediately preceeding application have enabled excellent clinical results to be obtained with a minimum of complications.