By the nineteenth century, it was recognized that zits were a disease of the sebaceous glands. But what caused the disease was the subject of wide speculation. Theories ranged from constitutional factors, mode of life, use of cosmetics, affections of the alimentary tract and, supposedly, abnormal sexual behavior. Sulfur containing concoctions were the standard treatment back then. Sulfur has a drying and exfoliative effect on the skin.
Throughout the years, as we gained more and more knowledge about the disease, treatments were developed in response to the latest scientific discoveries. According to News-Medical.net, here is a timeline of zit therapy:
1920's: benzoyl peroxide
1930's: radiation and laxatives
1970's: Retin A (tretinoin)
1980's: Accutane (found to cause birth defects in pregnant women)
1990's: laser therapy
2000's: blue/red light therapy