Use of reflectance near-infrared spectroscopy to investigate the effects of daily moisturizer application on skin optical response and barrier function.

A number of noninvasive techniques and instruments have emerged over the years allowing much progress toward clarifying the structure and function of human skin and studying the effects of various applied substances. All of this research has provided great insight into the interactions between skin and various products through quantitative and qualitative measurements. Such methods include near-infrared spectroscopy (NIRS), a technique which has gained popularity over the years and has often been employed to accurately determine the moisture levels and water content of skin based on its sensitivity to hydrogen bonding. NIRS has also been applied in many studies to report the efficacy of moisturizing products and assess their benefits to the skin. However, many of these studies have reported an increase in skin water content following moisturizer application while some have challenged the benefits of long-term moisturizer use, particularly on normal skin, and even suggested that it can increase the skin's susceptibility to irritants. This paper reports the results of a pilot in vivo study carried out on the skin of 20 healthy volunteers, categorized into groups depending on their skin type and frequency of moisturizer use, in order to investigate the optical response of human skin after direct short-term contact with water followed by application of a moisturizer. The measurements were obtained using a highly advanced spectrophotometer in the region of 900 to 2100 nm equipped with a customized reflectance fiber optic handheld probe. Scatter graphs of group results and second derivative spectra have shown an interesting pattern between frequent users of moisturizers and individuals who do not use moisturizers, suggesting that long-term daily moisturization may have an effect on skin barrier function. The results also raise some questions regarding the optical characteristics of different skin types, as well as the varying response between different water bands in the NIR region. Future work will focus on gaining more knowledge about these subjects and obtaining results from a larger population, as well as performing statistical analysis through regression methods in order to further improve optical skin measurements.