Benzoyl peroxide and tumorigenesis-Is there a connection?

Although benzoyl peroxide has been available for consumer use for three decades without any major reported side effects, we add a few comments regarding the safety of benzoyl peroxide at this time.

Benzoyl peroxide is metabolized to benzoic acid (which is in some beverages, for example) as it passes through the skin. In studies of excised skin, it is only benzoic acid that is recovered on the dermal side (JAAD 1981;4:31-37; JAAD 1983;6:920-926). From an in vitro monkey study, the benzoic acid recovered in the dermis then diffused into the circulatory system.

Benzoic acid does not appear to circulate to the liver, since no hippuric acid (the hepatic metabolite of benzoic acid) was recovered in the urine of monkeys after topical application of C14 labeled benzoyl peroxide (JAAD 1981;4:31-37; JAAD 1983;6:920-926). Benzoic acid accounted for 95.5 percent of the recovered C14 in the urine, and four minor metabolites accounted for the remaining 4.5 percent. Thus, once benzoic acid reaches the systemic circulation, it appears to undergo rapid renal clearance and essentially precludes passage through the liver. Also, benzoyl peroxide topically did not enhance UV tumorigenesis in hairless mice in two studies (JID 1986;86:442-448; Carcinogenesis 1988;9:803-809) despite the finding that benzoyloxy radicals and phenyl radicals are produced, which are thought to be pro-mutagenic.