Abstract
The phenomenon of aging can broadly be categorized into photoaging caused by exogenous factors and physiological aging that is caused by endogenous factors. Our goal was to develop a non-invasive way to assess changes taking place inside the skin for each type of aging, photoaging and physiological aging, by using near-infrared diffuse reflectance (NIR-DR) spectroscopy. For the photoaging and physiological aging effects, the outer forearm (sun-exposed) and the inner upper arm (sun-protected) skin areas were studied in eighty-six females from twenty-three to sixty-nine years of age. Measurements were made using NIR-DR and subjected to Principal Component Analysis (PCA) ; the results suggested the possibility of distinguishing and quantifying both types of aging taking place inside the skin by using the 1670-1820 nm and 2000-2230 nm regions of NIR-DR spectra. In photoaging, structural changes in proteins occur which are reflected in the NIR-DR spectra in the form of a peak shift near 2050 nm that is due to a combination of amide A and amide II. On the other hand, physiological aging is associated with a change in collagen quantity as is reflected in the portion of the NIR-DR spectra assigned to protein. Using NIR-DR and PCA, we discovered the possibility of using a non-invasive method for assessing the degree of photoaging and physiological aging as degeneration and degradation.
