Benzoyl peroxide was introduced as a basic treatment already in acne therapy 1934. The mechanism of action is the reduction of anaerobe bacteria by strong oxidation processes. No resistancies have been ever reported. BPO is available in 2.5, 5 and 10 % formulations. Its efficacy is slightly related to the strength of concentrations, but the side effect profile with burning, erythema and desquamation is increasing with concentrations. BPO 5% mostly is efficient enough to control acne of grades I to II according to the Kligman & Plewig classification. BPO my bleach clothes and hair. It is the most costeffective topical drug in acne of grades I-II. Inflammatory acne of the papular-pustular type I-II can also be treated by topical antibiotics such as erythromycin, clindamycin, and, less frequent and today not anymore recommended tetracyclines. Mechanism of action is not alone an antibacterial but anti inflammatory effect. The efficacy and penetration of the topical antibiotics between the groups are similar. Randomized studies have shown that concentrations of 2-4% are equivalent to oral tetracycline and minocycline in mild to moderate acne. Combinatory formulations with BPO and with retinoids enhance the efficacy significantly. Topical antibiotics plus BPO show less bacterial resistancies as topical antibiotics alone. Antibiotics should therefore not be used as monotherapy. Moreover gram negative folliculitis may develop. Azelaic acid is acting as an antimicrobial and can also reduce comedones. It can also be used in pregnancy and during the lactation period.