There has been some controversy recently about the tumour-promoting effect of benzoyl peroxide.2 These data  were based on the  induction  of tumours  in a tumour-sensitive strain of mice, which had been previously treated with 7,12-dimethylbenz[a]anthracene as initiator. Such animal studies are always disquieting but an investigation of available data performed by a group independent of the manufacturers indicated that benzoyl peroxide is almost certainly safe.3 No data from longterm follow-up studies in subjects who have received benzoyl peroxide are available.

 

  Some years ago there  was a similar concern about retinoic acid, with particular  reference to ultraviolet radiation (UVR) induced tumours - in animals.  Recent studies indicate that topical vitamin A is safe and in animals reverses the ageing  processes  induced by UVR.