生活中, 日光中的紫外辐射是导致头发光老化/光损伤的重要环境因素。 长时间光照可使染发和天然发出现包括颜色褪变在内的退行性变化。 以中老年人的自然灰发为样本来源, 通过分离和人工漂染处理, 获得了包括自然发色、 漂白和染黑的六种头发类型, 经过UVA(320～400 nm)紫外光老化, 采用漫反射光谱、 三维荧光光谱和衰减全反射傅里叶变换红外光谱对头发纤维的老化特征进行无损分析, 结合头发中光产生过氧化氢的定量分析, 探讨了不同发色和漂染处理对头发耐光性的影响。 结果表明, UVA辐照可通过Ⅱ型电子转移机制诱导头发中的光敏基团产生过氧化氢, 导致纤维表面蛋白和色素分子的光氧化降解。 自然发色与漂染发在光老化中的颜色变化不同: 灰发和白发主要发生光黄化, 人工染发和漂白发分别发生光褪色和光漂白。 高湿度环境能加速头发的光降解。 化学漂染处理会使头发中的光致过氧化氢水平升高, 使纤维处于较高的氧化压力从而影响头发的光稳定性; 而头发中的黑色素分子, 包括天然黑色素和染发剂的人工黑色素, 可能具有自由基产生与清除双重性。 研究结果为建立中国人头发光损伤的光谱学评价方法和进一步研发针对国人发质的染护发产品提供了重要的实验基准数据。

Since ultraviolet radiation is one of the major environmental factors that cause photoageing/photodamage, human hair, including both dyed and undyed hair, are subject to color change following extended exposure to sunlight. In the work described in this paper, six samples of human hair from Chinese volunteers that included untreated, bleached and dyed were subjected to accelerated ageing by exposure to UVA (320～400 nm) radiation. Changes to their chemical compositions during photoageing were non-destructively characterized by reflectance, 3D-fluorescence and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopies. These techniques, together with a quantitative analysis of the photosensitized generation of hydrogen peroxide, were used to assess the effects of different hair color and bleaching/dyeing treatments on the light stability of hair fibers. The results suggest that UVA irradiation can induce the production of hydrogen peroxide via a type Ⅱ mechanism (electron transfer interaction between photosensitive protein groups in their excited states) and subsequent reaction with oxygen, resulting in photo-oxidative degradation of surface protein and pigments of the hair fiber. Hair fibers of natural or artificial color respond differently in terms of color change during photoageing. Natural white and gray hair fibers exhibited the usual photoyellowing; and chemically black-dyed and bleached hairs showed photofading and additional photobleaching, respectively. Irradiation of hair in the wet state was found to accelerate photodegradation. Chemical bleaching and oxidative dyeing processes were shown to promote the photoinduced production of hydrogen peroxide, which contribute to a higher level of oxidative stress and thereby affects the photostability of human hair. Pigment molecules in hair, including both the natural pigmentation of melanin and that produced by artificial dyes, are suggested to play a dual role, both in the production and in the scavenging of oxygen free radicals. The work is designed to contribute to the establishment of spectroscopic methods for assessing the extent of hair photodamage as well as providing a sound experimental data basis for the research and development of improved hair dyes and after-dye products for the Chinese cosmetic market.