Reactive oxygen species generated in dermal cells of human skin is related to skin disorders or diseases. In this study, Raman analysis effectively clarified the identities of three types of human skin models after the models were stimulated with hydrogen peroxide. With the Caucasian skin model, the major Raman bands underwent large intensity changes within 4-5 days of stimulation. With the Black skin model, the Raman bands remained almost unchanged. The changes in the Asian skin model were unique compared to those in the above two. Eumelanin and pheomelanin are probably the main compounds that differentiate dermal cells in terms of their sensitivity to hydrogen peroxide. 1. Introduction Human skin is sensitive to sunlight, especially to ultraviolet (UV) light, which generates reactive oxygen species (ROS) in dermal cells. This phenomenon is related to disorders or diseases such as stains, freckles, and cancers of the skin. Many researchers have sought to understand these disorders at the molecular level and are also interested in classifying them [1–3]. In clinical medicine, Raman spectroscopy attracts researchers as a microscopic, nondestructive, and nonlabeling research tool. Raman spectroscopy provides information about the compositions, structures, and interactions of molecules [4], and it has been used as a powerful analytical method in chemistry for 80 years. Its application to clinical medicine has been somewhat slower, beginning during the 1970s [5–7], when the development of a Raman microscope allowed effective spectral measurements of biological tissues [8–11]. Today, we can measure the Raman spectrum of a live cell (ca. 20？μm in width) with high spectral quality, distinguishing an area of 1？μm2 in the horizontal plane (ca. 30？s for the spectrum) [12, 13]. Moreover, the use of a flexible fiber is one of the most promising approaches for making noninvasive Raman measurements of living tissues, and several research groups have developed fiber optics suitable for Raman measurements [14–19]. In this study, three-dimensional (3D) human skin models were stimulated with hydrogen peroxide (H2O2) to provide time-dependent Raman spectra. As mentioned above, UV-visible light generates ROS in dermal cells. H2O2, one of typical ROS, was therefore used as a substitute for UV light to stimulate the skin models. The 3D human skin models consisted of keratinocytes, melanocytes, and a collagen-layered membrane, as shown in Figure 1(a), which are frequently used for skin irritation tests in dermatology. Three kinds of skin models, containing Caucasian, Asian,
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