What it is
Salicylic acid is an oil-soluble beta hydroxy acid that helps loosen and shed surface skin cells, which is why it is common in products aimed at oily or blemish-prone skin. Because it can penetrate sebum, it is favored for working within pores. At low concentrations it can also serve as a preservative in cosmetic formulas. Its use level and labeling are regulated as a cosmetic ingredient in several markets.
Safety & warnings
Well studied and generally well tolerated at cosmetic levels, though it can cause dryness, stinging, or irritation, especially on sensitive or compromised skin or when combined with other exfoliating acids. Use levels are restricted by regulation in several markets, and it is not recommended for use on infants. It is non-comedogenic and is not classed as a fragrance allergen.
Origin & sourcing
Synthetic for cosmetic use, although salicylates occur naturally; willow bark and wintergreen are historic natural sources of related compounds.
History
Salicylic acid takes its name from the willow (Salix), whose bark was a long-used folk remedy; the purified acid was characterized in the 19th century and later became a staple of dermatological and cosmetic formulation.
Questions everyone asks
Is salicylic acid the same as an AHA?
No. Salicylic acid is a beta hydroxy acid (BHA) and is oil-soluble, whereas alpha hydroxy acids such as glycolic and lactic acid are water-soluble and work differently on the skin surface.
Why is it in a sunscreen?
It is usually included for its exfoliating or skin-conditioning role, often in formulas targeting oily skin, and can also help preserve the product at low concentrations.