Changes in the depth profile of water in the stratum corneum treated with water

Abstract

Water in the stratum corneum (SC) plays an important role in keeping the skin surface soft and smooth. Information regarding the depth profile of the molecular composition of the skin, such as water and free amino acids, can be obtained non-invasively using the recently developed confocal Raman spectrometer. In this study, we investigated changes in the depth profile of water in the SC treated with water. We also unveil a relationship between the depth profile patterns of water content in the SC and cutaneous sensation. Depth profiles of Raman spectra in the region 2600-4000 cm(-1) were obtained using a 671-nm laser at 2 mum intervals from the skin surface toward the interior with a confocal Raman spectrometer. Water content (mass%), expressed in grams of water per 100 g wet tissue, was calculated from the water-to-protein ratio of the Raman band. Skin surface temperature was measured by an infrared irradiation thermometer. Changes in the depth profile of water and skin temperature were measured at 1, 5, and 10 min after the application of water to the skin surface. In addition, questionnaires regarding cutaneous sensation were administered. Water content in the middle to lower part of the SC increased with increased water-application time. Warming of the skin during water application increased the water-penetration amount, depth, and holding time in the SC. Steamer application increased water content particularly in the upper part of the SC. Increasing water content in the upper part of the SC was associated with cutaneous sensations, such as hydrate and water-rich feelings. On the other hand, the increasing water content in the middle and lower part of the SC was associated with water penetration and tension feelings. The water content in the upper part of the SC changed easily. When water was applied externally, the water content in both the upper and middle/lower part of the SC increased with increasing water-application time. In addition, warming of the skin during water application increased the water-penetration depth, amount, and holding time of water in the SC. Thus, we were able to control the depth profile of water in the SC by externally applying water. The location of water in the SC also affected cutaneous sensations.