Benzoyl peroxide is the single most effective anti-acne topical ingredient. The American Academy of Dermatology acne treatment guidelines places benzoyl peroxide on the top of the list of suggested anti-acne medications. Other ingredients such as retinoids (Differin, adapalene) and azelaic acid are significantly less effective for the treatment of active acne. To your question: The skin around the mouth and on the neck, is very sensitive. Do NOT apply creams with benzoyl peroxide (or adapalene) to these areas. Wash your hands after you use these creams. This will avoid touching, and spreading the creams to the neck by mistake.