Hi, Duac Once Daily Gel contains both clindamycin and benzoyl peroxide as its active ingredients. It is used to treat as well as prevent acnes by reducing the growth of bacteria or germs which are responsible for acnes, decreasing the acne spots, limiting the chance of new whiteheads or blackheads formation and reducing the oiliness of skin. Side effects of Duac Once Daily Gel are peeling, dry skin, erythema, pruritus, sunburn, skin pain, stinging as well as burning sensation, allergic reactions at the site of topical application. In some rare cases, clindamycin may be the main culprit for causing reproducible ringing in the ear, tinnitus, hearing loss and severe headaches at the side of head where the ear ringing occurred first. If you suffer from such type of side effects, then you should inform your doctor immediately for medical help and further evaluation. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Zubayer Alam, General And Family Physician