In vivo sun protection factor and UVA protection factor determination using (hybrid) diffuse reflectance spectroscopy and a multi‐lambda‐LED light source

The sun protection factor (SPF) values are currently determined using an invasive procedure, in which the volunteers are irradiated with ultraviolet (UV) light. Non‐invasive approaches based on hybrid diffuse reflectance spectroscopy (HDRS) have shown a good correlation with conventional SPF testing. Here, we present a novel compact and adjustable DRS test system. The in vivo measurements were performed using a multi‐lambda‐LED light source and an 84‐channel imaging spectrograph with a fiber optic probe for detection. A transmission spectrum was calculated based on the reflectance measured with sunscreen and the reflectance measured without sunscreen. The preexposure in vitro spectrum was fitted to the in vivo spectrum. Each of the 11 test products was investigated on 10 volunteers. The SPF and UVA‐PF values obtained by this new approach were compared with in vivo SPF results determined by certified test institutes. A correlation coefficient R2 = 0.86 for SPF, and R2 = 0.92 for UVA‐PF were calculated. Having examined various approaches to apply the HDRS principle, the method we present was found to produce valid and reproducible results, suggesting that the multi‐lambda‐LED device is suitable for in‐vivo SPF testing based on the HDRS principle as well as for in‐vivo UVA‐PF measurements. A UV‐LED based system was developed that is suitable to determine UV reflectance spectra of skin with sunscreen products in a non‐invasive way in vivo. Sun protection factors can be calculated based on in vivo data combined with in vitro data. The measurement setup is compact and adjustable.