Evaluating sunscreen ultraviolet protection using a polychromatic diffuse reflectance device

BACKGROUND: Sun protection factor (SPF) and UVA protection factor (UVA‐PF) are determined using in vivo tests, with high exposures of subjects to ultraviolet (UV) radiation. Hybrid diffuse reflectance spectroscopy (HDRS) enables estimation of both indices using only trace amounts UVB. However, the equipment requires two expensive monochromators that must synchronously scan the spectrum. METHODS: An alternate approach was developed using a polychromatic source that illuminates the skin via a custom light guide array, and the diffuse reflected light is measured with a photomultiplier. The ratio of the diffuse reflectance with and without the sunscreen on the skin determines the polychromatic diffuse reflectance UVA‐PF (PDRS UVA‐PF(0)). This factor was used to adjust in vitro UV spectroscopy scans of the sunscreen (with and without UV exposure to assess photostability), to calculate SPF and UVA protection factors. Ten sunscreens were evaluated and compared to in vivo SPF and UVA‐PF values. RESULTS: The data show an excellent correlation with known in vivo determinations. CONCLUSION: This polychromatic HDRS approach uses simpler, faster, and less expensive equipment to determine both UVA‐PF and SPFs without high doses of UV radiation to the test subjects.