In the skin follicle, benzoyl peroxide kills C. acnes by oxidizing its proteins through the formation of oxygen free radicals and benzoic acid. These free radicals likely interfere with the bacteriums metabolism and ability to make proteins. Additionally, benzoyl peroxide is mildly effective at breaking down comedones and inhibiting inflammation. Combination products use benzoyl peroxide with a topical antibiotic or retinoid, such as benzoyl peroxide/clindamycin and benzoyl peroxide/adapalene, respectively. Topical benzoyl peroxide is effective at treating acne.Side effects include increased skin photosensitivity, dryness, redness, and occasional peeling. Sunscreen use is often advised during treatment, to prevent sunburn. Lower concentrations of benzoyl peroxide are just as effective as higher concentrations in treating acne but are associated with fewer side effects. Unlike antibiotics, benzoyl peroxide does not appear to generate bacterial antibiotic resistance. Retinoids
Retinoids are medications that reduce inflammation, normalize the follicle cell life cycle, and reduce sebum production. They are structurally related to vitamin A. Studies show dermatologists and primary care doctors underprescribe them for acne. The retinoids appear to influence the cell life cycle in the follicle lining. This helps prevent the accumulation of skin cells within the hair follicle that can create a blockage. They are a first-line acne treatment, especially for people with dark-colored skin. Retinoids are known to lead to faster improvement of postinflammatory hyperpigmentation.Topical retinoids include adapalene, retinol, retinaldehyde, isotretinoin, tazarotene, trifarotene, and tretinoin. They often cause an initial flare-up of acne and facial flushing and can cause significant skin irritation.
True cysts are rare in those with acne, and the term severe nodular acne is now the preferred terminology.Acne inversa (L.  invertō, "upside-down") and acne rosacea (rosa, "rose-colored" + -āceus, "forming") are not forms of acne and are alternate names that respectively refer to the skin conditions hidradenitis suppurativa (HS) and rosacea. Although HS shares certain overlapping features with acne vulgaris, such as a tendency to clog skin follicles with skin cell debris, the condition otherwise lacks the hallmark features of acne and is therefore considered a distinct skin disorder. Signs and symptoms
Typical features of acne include increased secretion of oily sebum by the skin, microcomedones, comedones, papules, nodules (large papules), pustules, and often results in scarring. The appearance of acne varies with skin color. It may result in psychological and social problems. Scars
Acne scars are caused by inflammation within the dermis and are estimated to affect 95% of people with acne vulgaris. Abnormal healing and dermal inflammation create the scar. Scarring is most likely to take place with severe acne but may occur with any form of acne vulgaris. Acne scars are classified based on whether the abnormal healing response following dermal inflammation leads to excess collagen deposition or loss at the site of the acne lesion.Atrophic acne scars have lost collagen from the healing response and are the most common type of acne scar (accounting for approximately 75% of all acne scars). Ice-pick scars, boxcar scars, and rolling scars are subtypes of atrophic acne scars.