Exposure to oxybenzone from sunscreens: daily transdermal uptake estimation

Background Fugacity, the driving force for transdermal uptake of chemicals, can be difficult to predict based only on the composition of complex, non-ideal mixtures such as personal care products. Objective Compare the predicted transdermal uptake of benzophenone-3 (BP-3) from sunscreen lotions, based on direct measurements of BP-3 fugacity in those products, to results of human subject experiments. Methods We measured fugacity relative to pure BP-3, for commercial sunscreens and laboratory mixtures, using a previously developed/solid-phase microextraction (SPME) method. The measured fugacity was combined with a transdermal uptake model to simulate urinary excretion rates of BP-3 resulting from sunscreen use. The model simulations were based on the reported conditions of four previously published human subject studies, accounting for area applied, time applied, showering and other factors. Results The fugacities of commercial lotions containing 3–6% w/w BP-3 were ~20% of the supercooled liquid vapor pressure. Simulated dermal uptake, based on these fugacities, are within a factor of 3 of the mean results reported from two human-subject studies. However, the model significantly underpredicts total excreted mass from two other human-subject studies. This discrepancy may be due to limitations in model inputs, such as fugacity of BP-3 in lotions used in those studies. Significance The results suggest that combining measured fugacity with such a model may provide order-of-magnitude accurate predictions of transdermal uptake of BP-3 from daily application of sunscreen products.