Also called beta hydroxy acid (BHA), this multifunctional ingredient addresses many of the systemic causes of acne. Its primary benefit is as an exfoliant, helping shed dead skin in a way similar to how skin acts when we are younger. Because it has the ability to penetrate into the pore lining and exfoliate inside the pore as well as on the surface of skin, it is especially effective for reducing breakouts, including blackheads and whiteheads.
In addition to these benefits, salicylic acid also has soothing properties to calm aggravated skin, can help minimize the appearance of an uneven skin tone, and has hydrating abilities that can result in smoother skin.
References for this information:
Clinical, Cosmetic, and Investigational Dermatology, November 2010, pages 135-142
Seminars in Cutaneous Medicine and Surgery, September 2008, pages 170-176
Journal of the American Academy of Dermatology, April 2007, pages 651-663
International Journal of Cosmetic Science, February 2000, pages 21-52
Seminars in Dermatology, December 1990, pages 305-308.