46.    Ultraviolet light induced hair shaft damage after hair dyeing. 
Soo Young Jeon, Long Quan Pi, Won-Soo Lee, Department of Dermatology and Institute of Hair and Cosmetic Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea.

Human scalp hairs protect scalp skin from sunlight, and eyebrows and eyelashes keep our eyes from solar damage and sweat. Also, human hairs have important meaning related to body image in social life. Entering the modern society, industries related with hair cares and hair health have been developed continuously. Accordingly, there have been increasing needs about scientific research of hair.
The causes of external hair shaft damage are various, and roughly it can be grouped as physical causes and chemical causes. Physical causes are mainly composed of heat stimuli during artificial hair drying and exposure to sunlight. On the other hand, chemical agents for permanent waving, bleaching and dyeing are well known causes of chemical hair damage. In our previous study, hair dyeing process induced hair cuticle detachment and intercellular lipid layer damage, and those conditions seemed to recover gradually after 1 week. Among the various causes of damage, sunlight, especially ultraviolet light induced hair damages are inescapable during daily life. Many scientists have studied about photoaging in skin, but concerns about the effects of ultraviolet light to hair have been emerging recently. Hairs exposed to ultraviolet light tend to be dry, coarse and stiff, and usually lose their strength, color and luster. These photochemical changes are mainly known to come from damages of hair proteins and melanins. Particularly, ultraviolet light of 254-400nm can damage to hair protein by oxidation of sulfur-containig molecules on the hair shaft. In this study, we investigated the patterns of morphological and moleculobiological changes from artificial ultraviolet light-induced photo-damaged hairs after hair dyeing by scanning and transmission electronmicroscopy and hair protein analysis. In results, hair soluble protein changes were induced mainly after UVA radiation, while structural changes such as hair cuticle damage were induced mainly after UVB radiation.