Solar radiation has been accepted as a major contributor to the development of skin cancer. Recent studies have shown that visible light (VL), a major portion of solar spectrum, induces biologic effects. UV filters in currently available sunscreens do not offer protection against VL. Diffuse reflectance spectroscopy (DRS) is a noninvasive objective assessment technique. Previous studies have focused on physiological parameters including melanin concentration, hemoglobin concentration, scattering and oxygen saturation. However, the differential absorbance spectra, difference between absorbance spectra of irradiated site and adjacent un-irradiated skin, can aid in the identification of various phases of skin response after VL irradiation. We irradiated the back of 62 subjects with a VL source, which consisted of a halogen lamp with filters resulting in a spectral output with greater than 98% VL. Reflectance spectra was collected for VL irradiated sites (160 J/cm2 to 480 J/cm2) immediately post-irradiation, at 24 hours, and at 7 days post-irradiation. DRS aided in classifying skin responses in terms of clinical and sub-clinical erythema accompanied by pigmentation phases based on the corresponding spectral signatures. The response in terms of skin darkness was assessed by integrating the differential absorbance spectra between 400 and 700 nm (AUC, area under the curve) since it includes contribution from both melanin and hemoglobin. The findings demonstrate the potential of DRS in assessing photoprotection offered by a product against VL induced pigmentation and erythema, VL protection factor, which can be assessed by comparing the AUC of the protected skin to that of the unprotected skin.
Indermeet Kohli, Tasneem F. Mohammad, Cynthia L. Nicholson, Nikiforos Kollias, Henry W. Lim, and Iltefat Hamzavi, "In vivo characterizations of optical properties of human skin responses to visible light by diffuse reflectance spectroscopy (Conference Presentation)," Proc. SPIE 10467, Photonics in Dermatology and Plastic Surgery 2018, 104670V (Presented at SPIE BiOS: January 28, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2290175.5751326336001.
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