A comparative study of the in vitro dermal absorption of radiolabeled benzophenone through human skin

Octocrylene is a common sun filter ingredient used to protect the skin from damaging UV rays. Benzophenone is an impurity found in formulations containing octocrylene. [¹⁴C]-Benzophenone was spiked (0.1 g/L) into 2 commercial sunscreen formulations; Neutrogena® Beach Defense Sunscreen Spray Broad Spectrum SPF 70 Aerosol, Neutrogena® Ultra Sheer Body Mist Sunscreen Broad Spectrum SPF 30 Aerosol, and an acetone vehicle. The formulations were applied (ca 2 μL/cm²) to dermatomed human skin mounted in static diffusion cells in vitro. Receptor fluid was collected up to 24 h post dose. All samples were analyzed by liquid scintillation counting. The dermal delivery of [¹⁴C]-Benzophenone was 10.02, 9.04 and 5.19% for the 3 formulations. However, the [¹⁴C]-Benzophenone mass balances were low; 81.5, 85.3 and 8.02%, respectively. A volatility test was performed replacing skin with aluminum foil for the sunscreen formulations only. The [¹⁴C]-Benzophenone mass balance at dosing was 99% but fell to 56.9 and 60.6% at 24 h post dose, confirming the losses were due to [¹⁴C]-Benzophenone volatility. A conservative dermal absorption value of 12.42% was proposed to cover [¹⁴C]-Benzophenone containing formulations.