水楊酸
Salicylic acid is a topically applied beta-hydroxy acid that stops bacteria from reproducing and has keratolytic properties. It is less effective than retinoid therapy. Salicylic acid opens obstructed skin pores and promotes the shedding of epithelial skin cells. Dry skin is the most commonly seen side effect with topical application, though darkening of the skin can occur in individuals with darker skin types.