Benzac AC (Benzoyl Peroxide) is used to treat mild to moderate acne. It may be used in combination with other acne treatments. When applied to the skin, benzoyl peroxide works by reducing the amount of acne-causing bacteria and by causing the skin to dry and peel. Check the ingredients on the label even if you have used the product before. The manufacturer may have changed the ingredients. Also, products with similar names may contain different ingredients meant for different purposes. Taking the wrong product could harm you.