Benzoyl peroxide is the single most effective anti-acne medication (prescription and OTC) available. It works as an anti-bacterial agent by producing free oxygen that kills the acne bacteria and also has some exfoliating properties to unclog the obstructed skin pores.
Salicylic acid is a milder (but still very effective) anti-acne agent. It can sometimes be a better fit for people with more sensitive skin who have primarily comedones (blackheads and whiteheads) and can be particularly helpful for women with adult acne. Its main effect is to unclog skin pores, prevent blackheads and whiteheads, and also provides some anti-inflammatory effects.
Both benzoyl peroxide and salicylic acid are medications that should be used at night. The application is the same - a small amount of the cream spread evenly on the whole face. To prevent over dryness, do not apply the products around the eyes and on the skin folds (sides of the nose and the mouth). In the morning, you need to apply an oil-free moisturizer or sunscreen to further reduce skin dryness and protect from the sun.