Benzoyl peroxide causes cancer.

  Years ago, safety concerns with benzoyl peroxide were raised when rodent studies suggested that it increased the development of skin cancer.

  This prompted the FDA to reclassify benzoyl peroxide from Category I (safe and effective) to Category III (more-data needed). But it was decided that the data weren't compelling enough to warrant pulling benzoyl peroxide from the market. Other studies did not show benzoyl peroxide to be a carcinogen. But the FDA wanted more evidence that it was not a weak, slow-acting one.

  Meanwhile, drug labeling for products containing benzoyl peroxide were changed to reflect the carcinogenic potential in animals. And because sun exposure is another known risk factor for skin cancer, users of benzoyl peroxide were also advised to avoid the sun or to use a sunscreen.