Near-infrared spectroscopy: A new approach to the characterization of dry skin

In a first set of in vitro experiments, we examined the penetration of IR waves into the various skin layers. The results showed the role of the stratum corneum (SC) in the amplitude of the two water peaks and that the amplitude is proportional to the water content. The dry skin type known as winter xerosis is characterized by a marked alteration of the appearance and surface state of the SC. This led us to describe the clinical condition in terms of the following criteria: inflammation, roughness (smooth/rough), and presence of flakes and scales. We attributed a score of 0-4, and an overall score was then calculated. The water content of the skin was measured in the same area (external surface of the leg) in a number of subjects, using two biophysical methods--near-infrared spectroscopy and an electrical conductance method that provides only a very indirect measurement of water content. Correlations between the biophysical measurements and the clinical scores showed clearly that the skin judged as being the dryest gave the lowest peak amplitudes in the near infrared. This correlation was much better than that obtained using the clinical scores and the conductance method, particularly for very dry skin. A more thorough analysis of the correlations between the clinical scores and the NIR parameters provides further information on this phenomenon.