Hi Neha, thanks for asking in Healthcare Magic. Acne is hormonal. Under androgenic influence excess of sebum is produced in sebaceous glands and get infected by bacteria resulting in acne. But do not use any hormonal preparations for it as they can result in many side effects on long term use. Benzyl peroxide is the most effective drug for acne. By liberating oxygen it kills the bacteria responsible for acne. It reduces the dark spots (black head) of acne. It reduces sebum production. Side effects are excessive dryness of skin, redness (erythema), swelling and contact dermatitis (allergy). How long you use it depends upon the degree of irritation it produces and the tolerance of your skin to it. You should discontinue if the side effects occur and persist. Clindamycin is less effective than Benzyl peroxide. Effective mainly in infected acne. It should not be used on long term even as topical application. So you should stop Clindamycin. Other preparations like Adapalene and Retinoic acid are less effective than Benzyl peroxide. Azelaic acid is a natural product and is used as topical application in acne. Though there is delayed response its effect is comparable to Benzyl peroxide. If you develop side effects to Benzyl peroxide, then you can switch over to Azelaic acid. I hope this is useful.