Acne

Acne vulgaris is a chronic inflammatory dermatosis of the pilosebaceous unit driven by four pathogenic factors: androgen-mediated sebaceous gland hyperactivity (increased sebum production under influence of dihydrotestosterone converted from testosterone by 5-alpha reductase in sebaceous glands), follicular hyperkeratinization (abnormal keratinization of the follicular infundibulum creates the microcomedo -- the precursor lesion), Cutibacterium acnes colonization (anaerobic bacterium that thrives in the lipid-rich, oxygen-poor environment of the obstructed follicle, producing lipases that generate pro-inflammatory free fatty acids and activating toll-like receptor 2 and inflammasome pathways), and inflammation (innate and adaptive immune responses to C. acnes and follicular rupture). The clinician classifies acne severity to guide treatment: mild (comedonal -- open and closed comedones with few inflammatory papules, treat with topical retinoid plus or minus benzoyl peroxide), moderate (papulopustular -- numerous papules and pustules, add topical antibiotic such as clindamycin always combined with benzoyl peroxide to prevent resistance), and severe (nodulocystic -- deep painful nodules, cysts, risk of scarring, consider oral isotretinoin or referral to dermatology). The clinician prescribes isotretinoin understanding its mechanism (substantially reduces sebaceous gland activity and sebum production, normalizes follicular...