In Vitro Evaluation of Potential
Protection Provided by Topical Products against Full Solar and Visible plus Infrared Radiation
Visible (VIS) and infrared (IR) portions of the solar spectrum are increasingly recognized as contributors to skin damage from sun exposure. In vitro testing methodologies were developed to qualitatively and semi-quantitatively rank protective properties of finished goods products against full solar, or VIS plus IR radiation. These methodologies utilize HD6 polymethylmethacrylate plates; simulated sunlight source with mirrors and cut-off filters to produce full solar or VIS plus IR irradiation – in conjunction with pyranometer; and monochromator-based spectrophotometer with wavelength range extending to 1100 nm. An expanded protection wavelength (EPW) definition and metric are proposed to measure the breadth of the protection of topical products against UV, VIS and partial IR-A irradiation range of the solar spectrum. EPW metric could be enhanced when the action spectra of photodamage, oxidative damage and photoageing caused by VIS and IR irradiation in the skin are more researched and become available.
Natural sun light at Earth surface has different amounts of Ultraviolet (UV, 290-400 nm) ~ 7%, Visible (VIS, 400~780 nm) ~ 55%, and Infrared (IR, >780 nm) ~40 %radiation (1). There are no precise limits for the spectral range of VIS since they depend upon the amount of radiant power reaching the retina and the responsivity of the observer (2).
IR radiation is composed of the wavelengths that are longer than those for VIS, from about 780 nm to 1 mm. For IR, the range between about 780 nm and 1 mm is subdivided into: IR-A: 780 nm to 1400 nm, IR-B: 1400 nm to 3000 nm; and IR-C: 3000 nm to 1 mm (3).
For many years sun care research has focused primarily on the damaging effects of UV radiation on skin. However, more than 90% of tot