Salicylic acid is a Beta Hydroxy Acid derived from willow tree bark that is used to stimulate the exfoliation of dry, outer-skin layers. It is especially effective for acne-prone, oily skin since it is able to penetrate the waxy plugs that clog pores, causing pimples. Salicylic Acid may be preferable to other popular acne ingredients like benzoyl peroxide which do not exfoliate as effectively or penetrate the waxy plugs in the acneic pores. Concentrations of 2% or more are most effective. A light moisturizer may be used to off-set any dryness that may occur with use.