Chemical UV filters approved for use in US sunscreen formulations are under increasing scrutiny due to their potential undesirable effects on human health and the environment. Concerns exist over long-term endocrine disruption and developmental toxicity that the sustained use of sunscreens might pose. Plant-based hydroxycinnamic acids (HCAs) and their corresponding esters are safer alternatives, and are known to absorb in the UVB-UVA (290–400nm) region of solar radiation. This study sought to evaluate and compare the potential of HCA esters for use as main UV filters in sunscreens using as performance benchmark existing commercial UV filters.

In the first phase of the project, three naturally occurring HCAs, ferulic acid, sinapic acid, and 3,4-Dimethoxycinnamic acid were each converted into their respective esters by Fischer esterification under microwave irradiation, using alcohols of increasing molecular weight C2-C5. Following isolation and purification by column chromatography, each ester product was incorporated in 8% weight in combination with up to 3% avobenzone into a sunscreen emulsion and subsequently applied as thin film in polymethylmethacrylate plates.  The ability to block solar radiation was measured via UV transmittance spectroscopy prior and after irradiation under a solar simulator. Proliferation assays of new compounds were performed on human skin cell.  HCA esters were found to be non-toxic, and typically less toxic than commercial counterparts.

We have shown that sunscreens containing approximately 8% weight of any one ester with 3% avobenzone compare well a commercial broadband sunscreen with SPF+50 containing 22.5% of a mixture of homosalate, octisalate, and octocrylene with 3% avobenzone. Calculated sun protection parameters were within 90-95% of the corresponding values of the commercial sunscreen. The in vitro data generated from this study suggest that each of the naturally sourced HCA-esters has the potential to replace of reduce the use of three commercial synthetic UV filters.