The sebaceous glands are stimulated by androgens produced in the skin itself. This explains why elevated androgen levels are seldom found in blood and urine from patients with acne. The most potent androgen is dihydrotestosterone (DHT), which is formed in the target cells, i.e. in the sebaceous glands, by a 5 alpha-reduction of testosterone. DHT is then bound to a specific receptor protein and translocated into the cell nucleus. In young persons genetically predisposed to acne a temporarily increased local DHT-formation has been postulated. In women androstenedione appears to be the major pre-hormone for DHT-formation. Adrenal androgens may account for prepubertal acne. Estrogens and progesterone influence acne only in high, unphysiological doses. Therapeutically we are waiting for a safe effective anti-androgen for topical use.