salicylic acid is a monohydroxybenzoic acid, a type of phenolic acid and a beta hydroxy acid.

This colorless crystalline organic acid is widely used in organic synthesis and functions as a plant hormone.

It is derived from the metabolism of salicin.

In addition to serving as an important active metabolite of aspirin, which acts in part as a pro drug to salicylic acid, it is probably best known for its use as a key ingredient in topical anti-acne products. 

salicylic acid works as a keratolytic, comedolytic and bacteriostatic agent, causing the cells of the epidermis to shed more readily, opening clogged pores and neutralizing bacteria within, prebenting pores from clogging up again by constricting pore diameter and allowing room for new cell growth.