Willow bark contains naturally-occurring salicylic acid. Salicylic acid works as an exfoliating acid to dissolve the keratin that binds the outermost layers of the skin, encouraging the natural exfoliation process of the skin. Due to its oil-soluble form, salicylic acid can penetrate inside the pore, to clear out dead skin cell build up and prevent comedones (blocked pores) from occurring, or acne-causing bacteria to overpopulate within the pore. This P.Acnes bacteria is anaerobic so needs an oxygen-free environment to thrive, and thus require a pore to be blocked.