Acne primarily affects areas with increased sebaceous glanddensity, such as the face, upper chest, and back. Superficialplugging of the pilosebaceous unit results in noninflammatorysmall (1to 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 nodulesrepresent 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).
The mainstays of treatment of acne are topical keratolytic agents and topical antibiotics. Creams, lotions, gels, foams, and solutions are available. Gels and solutions are commonly used because acne skin is generally greasier and these agents tend to be drying, but they have the tendency to be irritating and may not be as well tolerated. Creams and lotions are better tolerated but may not be as effective.
The keratolytic agents (salicylic acid, azelaic acid, tretinoin, adapalene, tazarotene) produce superficial desquamation and, subsequently, relieve follicular obstruction. They are a mainstay of first-line therapy. The topical retinoids (tretinoin, adapalene, tazarotene) are based on the vitamin A molecule. They decrease keratin and sebum production and have some anti-inflammatory and antibacterial activity; thus they can be the most effective when used as monotherapy.
Topical antimicrobials (benzoyl peroxide, dapsone, sulfur-sulfacetamide) and topical antibiotics (erythromycin, clindamycin) are anti-inflammatory and inhibit P. acnes proliferation. Erythromycin efficacy has decreased as P. acnes has become increasingly resistant to this antibiotic; topical antibiotics should be combined with an antimicrobial such as benzoyl peroxide to prevent the development of resistance. Combination therapy of a topical keratolytic agent and a topical antimicrobial is more effective than either agent alone for inflammatory acne.
Oral antibiotics (tetracycline, doxycycline, minocycline) are typically used for deeper cystic lesions but should always be used in combination with a topical regimen. Tetracyclines are the most effective antibiotics because of their significant anti-inflammatory activity. As with topical erythromycin, oral erythromycin is rarely used because of bacterial resistance.