Safety of oxybenzone: putting numbers into perspective.

O xybenzone, an organic UV-B and short-wave UV-A filter, has been available for over 40 years; it is widely used in sunscreens and other consumer products in the United States. The Centers for Disease Control and Prevention has estimated the prevalence of oxybenzone exposure in the general US population to be 96.8%. In the past few years, oxybenzone has received increasing attention as a potentially harmful compound. Initial concerns arose when a report demonstrated systemic absorption of oxybenzone in humans at a rate of 1% to 2% after topical application. Similar or higher rates of cutaneous absorption in human subjects have been observed. The potential for biological effects, however, were first published in a study by Schlumpf et al demonstrating uterotropic effects in immature rats after oral administration of oxybenzone; it should be noted that the estrogenic effect detected was less than 1 million-fold of estradiol, the positive control used. Nonetheless, this study has served as the basis for considerable concern among the public. In assessing the potential for hormonal disruption in humans, we decided to place into perspective the doses of oxybenzone used by Schlumpf et al to achieve the 23% increase in uterine size reported in immature rats. We performed 2 calculations: (1) we determined the equivalent amount of sunscreen required to be used topically in humans to achieve the effective cumulative amount of oxybenzone orally administered to immature rats; and (2) we determined the number of years of daily application required to obtain the equivalent levels of oxybenzone that the experimental animals were exposed to.