It is recognized that reactive oxygen species (ROS) are responsible for skin damage due to UVB-radiation (UVB-R). However, the triggering substance(s) for ROS generation after UVB-R is uncertain with respect to the activation of NADPH oxidase (Nox), xanthine oxidase (XOD), and respiratory chain-chain reactions in mitochondria. As a first step in identifying the trigger(s) for UVB-induced ROS generation, we examined the relationship between Ca(2+) levels and ROS generation in HaCaT keratinocytes. UVB-R exposure of HaCaT keratinocytes resulted in an immediate elevation of ROS that recurred 7 hours later. This was accompanied by immediately elevated intracellular Ca(2+) . A Ca(2+) chelating agent, BAPTA, abolished the elevation of ROS after UVB-R completely. In addition, exogenous H(2)O(2) did not increase intracellular Ca(2+) levels. This suggests that intracellular Ca(2+) is the first trigger for UVB-induced ROS generation.Journal of Investigative Dermatology Symposium Proceedings (2009) 14, 50-52; doi:10.1038/jidsymp.2009.12.
Background
Sun protection factor (SPF) and UVA protection factor (UVAPF) are performance indicators consumers recognize for UV protective cosmetics such as sunscreens. However, on‐site application density affects actual UV protection, despite these indicators. To understand actual UV protection better, a more reliable manner is needed to verify application density for further discussion of photoprotection efficacy regarding public health.
Objectives
To estimate the UV protective efficacy of sunscreen in actual use based on the application density of UV protective cosmetics and the analysis of UV protective effect modulated by application density.
Method
The subjects applied the SPF‐labeled sunscreens as usual. We measured the application amount and area including any amount on their hands to calculate the average application density on the face. Also, sunscreens were applied at densities of 0.5, 1.0, and 2.0 mg/cm2. The SPF values were measured at each application site to evaluate the effect of application density on photoprotection efficacy.
Result
We established a method of measuring application density utilizing three‐dimensional photograph analysis. The median application density of the sunscreen applied in actual use was 1.33 mg/cm2. The measured SPF values decreased in association with the decreased application density of sunscreens. Based on the estimate assuming the first‐order correlation, the SPF value required to get the protective effect equivalent to a sunscreen with SPF 15, 30, or 50 at 2 mg/cm2 was calculated to be 23.8, 47.5, and 79.2, respectively, with the application density of 1.33 mg/cm2.
Conclusion
We demonstrated a reasonable procedure for estimating the photoprotection efficacy of sunscreens on the face. A suggestion was made to consider the application density for further discussion of photoprotection among consumers, especially for the long term with respect to public health.
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