Benzoyl Peroxide & Salicylic Acid Bar soap is formulated for the treatment of acne. Benzoyl Peroxide works best on red, pus-filled pimples. It works by removing excess oil and dead skin cells, and helps kill acne-causing bacteria beneath the skin. Salicylic Acid works best on blackheads and whiteheads. It works by removing dead skin cells which clog pores and contribute to acne breakouts.