Stamatas Georgios N, Kollias Nikiforos
Johnson and Johnson Consumer and Personal Products, Skillman, New Jersey 08558, USA.
J Biomed Opt. 2004 Mar-Apr;9(2):315-22. doi: 10.1117/1.1647545.
The chromatic characteristics of skin color arise from the interactions of light (primarily absorption and scattering) with the epidermis and the dermis. The primary light absorbers in skin are hemoglobin and melanin. Most of scattering is attributed to collagen fibers and in pigmented skin to melanosomes. Traditionally skin redness is considered to arise due to locally elevated concentrations of hemoglobin, whereas skin pigmentation is attributed to melanin. In this study we attempt to understand better the contributions of these chromophores to the perceived skin color using spectral analysis of skin color reactions induced by ultraviolet (UV) irradiation or pressure. In the first experiment 12 individuals with skin phototypes III-IV were irradiated on the back using a solar simulator with doses ranging from 0.7 to 3 MED. The skin reactions were evaluated on days 1, 7, 14, and 21 after irradiation. Evaluations included diffuse reflectance spectroscopy (DRS) and clinical assessment of the erythema and the pigment reaction. Apparent concentrations of melanin, oxy-, and deoxy-hemoglobin were calculated from the absorption spectra. In the second experiment the levels of deoxy-hemoglobin of the volar forearm of ten volunteers were selectively altered by either application of a pressure cuff or by topical application of 3% H(2)O(2). Changes in skin color appearance were documented by photography, colorimetry, and DRS. In the UV exposure experiment all reactions were dose dependent. Oxy-hemoglobin values increased to a maximum on day 1, correlating well with the clinical evaluation of erythema, and then decreased exponentially to base line. Melanin showed a significant increase on day 7 and remained relatively constant for the next 3 weeks, correlating well with the clinical evaluation of pigmentation (tanning). Deoxy-hemoglobin increased slightly on day 1 and remained elevated for the next 2 weeks. Thus, deoxy-hemoglobin correlated moderately with the clinical erythema scoring on day 1 only, while it contributes significantly to what is clinically perceived as skin tanning on days 7 and 14. Application of pressure below the diastolic level increased deoxy-hemoglobin concentration as measured by DRS. This increase corresponded to a decrease of a "pigmentation" parameter (based on the L()a()b(*) scale) in a similar fashion that has been documented for increases in melanin concentration. Topical H(2)O(2) application reduced deoxy-hemoglobin levels as measured by DRS. This reduction coincided kinetically with a visible skin blanching. Application of pressure or H(2)O(2) did not significantly alter the levels of oxy-hemoglobin or melanin. In this report we present compelling evidence that deoxy-hemoglobin significantly contributes to the skin color appearance. Blood pooling, expressed as increased deoxy-hemoglobin, can contribute to what is visually perceived as pigmentation. Furthermore, we present that measurement of its contribution to the skin color appearance can only be accomplished with DRS.
皮肤颜色的色度特征源于光线（主要是吸收和散射）与表皮和真皮的相互作用。皮肤中的主要光吸收物质是血红蛋白和黑色素。大部分散射归因于胶原纤维，而在色素沉着的皮肤中则归因于黑素小体。传统上，皮肤发红被认为是由于局部血红蛋白浓度升高所致，而皮肤色素沉着则归因于黑色素。在本研究中，我们试图通过对紫外线（UV）照射或压力诱导的皮肤颜色反应进行光谱分析，更好地了解这些发色团对感知到的皮肤颜色的贡献。在第一个实验中，使用太阳模拟器对12名皮肤光类型为III-IV的个体的背部进行照射，剂量范围为0.7至3 MED。在照射后的第1、7、14和21天评估皮肤反应。评估包括漫反射光谱（DRS）以及对红斑和色素反应的临床评估。根据吸收光谱计算黑色素、氧合血红蛋白和脱氧血红蛋白的表观浓度。在第二个实验中，通过使用压力袖带或局部应用3% H₂O₂选择性地改变10名志愿者掌侧前臂的脱氧血红蛋白水平。通过摄影、比色法和DRS记录皮肤颜色外观的变化。在紫外线暴露实验中，所有反应均呈剂量依赖性。氧合血红蛋白值在第1天增加到最大值，与红斑的临床评估密切相关，然后呈指数下降至基线。黑色素在第7天显著增加，并在接下来的3周内保持相对稳定，与色素沉着（晒黑）的临床评估密切相关。脱氧血红蛋白在第1天略有增加，并在接下来的2周内保持升高。因此，脱氧血红蛋白仅在第1天与临床红斑评分中度相关，而在第7天和第14天对临床上被视为皮肤晒黑有显著贡献。舒张压水平以下施加压力会使DRS测量的脱氧血红蛋白浓度增加。这种增加对应于一个“色素沉着”参数（基于Lab*标度）的降低，其方式与黑色素浓度增加时所记录的相似。局部应用H₂O₂会使DRS测量的脱氧血红蛋白水平降低。这种降低在动力学上与皮肤明显变白同时发生。施加压力或H₂O₂并未显著改变氧合血红蛋白或黑色素的水平。在本报告中，我们提供了令人信服的证据，证明脱氧血红蛋白对皮肤颜色外观有显著贡献。以脱氧血红蛋白增加表示的血液淤积可导致在视觉上被视为色素沉着。此外，我们表明，只有通过DRS才能测量其对皮肤颜色外观的贡献。
