Acne etiology, epidemiology and clinical manifestations

Etiology:  Acne vulgaris (or acne) is a chronic inflammatory disorder that affects areas with the greatest concentration of sebaceous glands, such as the face, chest, and back. The pathogenesis of acne is multifactorial. Gender, age, genetic factors, and environment are all major contributing factors. Stress may trigger acne, possibly by affecting hormone levels. There is no evidence linking chocolate, candy, or fried foods to acne. Acne is caused by chronic inflammation of the pilosebaceous unit (hair follicle with an associated sebaceous gland). The primary event in all acne lesions is the development of the micro-comedo, which results from the obstruction of the hair follicle with keratin, increased sebum production from sebaceous glands, and overgrowth of normal skin flora, leading to pilosebaceous occlusion and enlargement. Androgens are a potent stimulus of the sebaceous gland. The subsequent inflammatory component and pustule formation results from proliferation of Propionibacterium acnes, a commensal organism of the skin. The pathogenesis of acne thus involves three components: increased sebum production, hyperkeratosis, and bacterial proliferation. Effective treatment focuses on minimizing these factors.
Epidemiology: Acne is the most common skin disorder in adolescents, occurring in 85% of teenagers. The incidence is similar in both sexes, although boys often are more severely affected. Acne may begin as early as 8 years of age and may continue into adulthood.
Clinical manifestations:  Acne primarily affects areas with increased sebaceous gland density, such as the face, upper chest, and back. Superficial plugging of the pilosebaceous unit results in noninflammatory small (1- to 2-mm) open (blackhead) and closed (whitehead) comedones. An open comedo is less likely to become inflammatory than a closed comedo. Rupture of a comedo into
adjacent dermis and proliferation of P. acnes induce an inflammatory response and development of inflammatory papules and pustules. Larger, skin-colored or red cysts and nodules represent deeper plugging and cystic acne. Increased and persistent inflammation, especially with rupture of a deep cyst, increases the risk of scarring. The diagnosis of acne is usually not difficult because of the characteristic and chronic lesions. Laboratory studies and imaging studies are usually not necessary to diagnose acne. Screening tests may be necessary if there are signs of hyperandrogenism
due to polycystic ovarian syndrome (irregular menses, hirsutism, insulin resistance) or an underlying androgen- secreting tumor (irregular menses, hirsutism, deepening voice, clitoromegaly).