Skin pigmentation by solar ultraviolet radiation (UVR; ~295–400 nm) is well established. More recently, visible light (VL; 400–740 nm) has been shown to induce rapid pigmentation. Such pigmentation is thought to be caused by oxidative stress, which has associations with skin cancer and photoageing. However, the UVR-VL boundary region has been less well studied. The lower back of healthy Fitzpatrick skin type (FST) II-IV individuals was irradiated with increasing doses of narrow-band 385 nm and 405 nm radiation [1]. Pigmentation change was measured immediately, 6 h and 24 h post-irradiation using two reflectance spectroscopy devices and visual grading. Pigmentation was dose-dependently increased in all skin types and time points for both spectra. Two sunscreens, both labelled SPF 15 and UVA protective in the EU and USA (but with different Boots star rating in the UK, 2* vs 5*) were compared. Their formulations were identical apart from the addition of a new organic filter bis- (diethylaminohydroxybenzoyl benzoyl) piperazine (BDBP) that absorbs between 350 and 425 nm. The product that lacked BDBP provided minimal protection against pigmentation, but its addition provided almost complete protection. This demonstrates the needs to improve photoprotection at the UVR-visible border and for sunscreens to act as neutral density filters.
The same sunscreens were also assessed for their ability to prevent oxidative stress, gene expression for photoageing, inflammation and oxidative stress, DNA damage (“dark” cyclobutane pyrimidine dimers) in HaCaT keratinocytes and in vivo in healthy FST I-II volunteers. The formulation including the new filter provided significantly more protection than the conventional sunscreen for almost all endpoints tested. This demonstrates the requirement for improved photoprotection at the UVR-visible border region.