Are SPF and Critical Wavelength sufficient to measure efficacy of sunscreen products against sun induced skin damage?
The SPF in vivo testing evaluates protection of sunscreen products against erythema induced by the light source that accurately simulates a small portion of sunlight spectrum. The FDA requirements of CW in vitro testing and 370 nm criterion for broad-spectrum protection extend the measurement of sunscreen effectiveness against UVA. However, this criterion provides no motivation for manufacturers to develop products with higher CW values; and there is ongoing debate whether current CW threshold might be revised. ROS are the significant damaging factors associated with sun exposure, and action spectrum for their production extends into VIS and IR. Continuing research whether antioxidants could mitigate sunlight induced ROS generation and the utilization of testing methodologies mimicking end-usage conditions will foster the development of better sunscreen products.
According to the International Commission on Illumination (also known as the CIE) natural sun light that reaches the earth has different amounts of Ultraviolet (UV, 290-400 nm) ~ 6%, Visible (VIS, 400-800 nm) ~ 55%, and Infrared (IR 800-2450) ~40 % radiation (1). Sunscreen products are used to protect skin against damage from the sun's rays and in the USA sunscreen products are OTC drugs regulated by the Food and Drug Administration (FDA). In 2011 the FDA issued a Final Rule “Labeling and Effectiveness Testing; Sunscreen Drug Products for Over-the-Counter Human Use” stating that that complete measure of broad-spectrum protection provided by a sunscreen product can be determined by criteria of Critical Wavelength (CW), measuring breadth of UVB an