Exfoliants induce continuous mild drying and peeling by irritation, damaging superficial skin layers and inciting inflammation. This stimulates mitosis, thickening the epidermis and increasing horny cells, scaling, and erythema. Decreased sweating results in a dry, less oily surface and may resolve pustular lesions.
Resorcinol is less keratolytic than salicylic acid and, when used alone, is classified as the Food and Drug Administration (FDA) category II (not generally recognized as safe and effective). The FDA considers resorcinol 2% and resorcinol monoacetate 3% to be safe and effective when used in combination with sulfur 3% to 8%. Resorcinol is an irritant and sensitizer and should not be applied to large areas or on broken skin. It produces a reversible dark brown scale on some dark-skinned individuals
Salicylic acid is keratolytic, has mild antibacterial activity against P. acnes, and offers slight antiinflammatory activity at concentrations up to 5%. Salicylic acid is recognized by the FDA as safe and effective, but it may be less potent than benzoyl peroxide or topical retinoids.
Salicylic acid products are often used as first-line therapy for mild acne because of their available prescription. Concentrations of 5% to 10% can also be used by prescription, beginning with a low concentration and increasing as tolerance develops to the irritation. Salicylic acid is often used when patients cannot tolerate topical retinoids because of skin irritation.
Sulfur is keratolytic and has antibacterial activity. It can quickly resolve pustules and papules, mask lesions, and produce irritation that leads to skin peeling. Sulfur is used in the precipitated or colloidal form in concentrations of 2% to 10%.
Although it is often combined with salicylic acid or resorcinol to increase effect, use is limited by offensive odor and availability of more effective agents.
Retinoids reduce obstruction within the follicle and are useful for both comedonal and inflammatory acne. They reverse abnormal keratinocyte desquamation and are active keratolytics. They inhibit microcomedone formation, decreasing the number of mature comedones and inflammatory lesions.
Topical retinoids are safe, effective, and economical for treating all but the most severe cases of acne. They should be the first step in moderate acne, alone or in combination with antibiotics and benzoyl peroxide, reverting to retinoids alone for maintenance once adequate results are achieved. Side effects include erythema, xerosis, burning, and peeling.
Retinoids should be applied at night, a half hour after cleansing, starting with every other night for 1 to 2 weeks to adjust to irritation. Doses can be increased only after beginning with 4 to 6 weeks of the lowest concentration and least irritating vehicle.
Tretinoin (retinoic acid and vitamin A acid) is available as 0.05% solution (most irritating); 0.01% and 0.025% gels; and 0.025%, 0.05%, and 0.1% creams (least irritating). Tretinoin should not be used in pregnant women because of risk to the fetus.
Adapalene (Differin) is the topical retinoid of first choice for both treatment and maintenance therapy because it is as effective but less irritating than other topical retinoids. Adapalene is available as 0.1% gel, cream, alcoholic solution, and pledgets. A 0.3% gel formulation is also available.
Tazarotene (Tazorac) is as effective as adapalene in reducing noninflammatory and inflammatory lesion counts when applied half as frequently. Compared with tretinoin, it is as effective for comedonal and more effective for inflammatory lesions when applied once daily. The product is available as a 0.05% and 0.1% gel or cream.