Also called beta hydroxy acid (BHA), this multifunctional ingredient addresses many of the systemic causes of acne.
It has the ability to penetrate into the pore lining and exfoliate inside the pore as well as on the surface of skin, which makes it effective for reducing breakouts, including blackheads and whiteheads.
References for this information:
Seminars in Dermatology, December 1990, pages 305-308.
Seminars in Cutaneous Medicine and Surgery, September 2008, pages 170-176
Clinical, Cosmetic, and Investigational Dermatology, November 2010, pages 135-142
International Journal of Cosmetic Science, February 2000, pages 21-52