BackgroundGenetic factors account for the majority of differences in skin color and hair morphology across human populations. Although many studies have been conducted to examine differences in skin color across populations, few studies have examined differences in hair morphology.ObjectiveTo investigate changing of integral hair lipids after ultraviolet (UV) irradiation in three human ethnic groups.MethodsWe studied the UV irradiation induced hair damage in hairs of three human populations. UV irradiation had been performed with self-manufactured phototherapy system. Damaged hair samples were prepared at 12 and 48 hours after UVA (20 J/sec) and UVB (8 J/sec) irradiation. We evaluated the changes of hair lipid using scanning electron microscopy (SEM), transmission electron microscopy (TEM), lipid TEM and HP-TLC. After UV irradiation, hair surface damage was shown.ResultsAfrican hair showed more severe damage on hair surface than others. The lipid compositions across human populations were similar, but Asian hair had more integral hair lipids than other groups as a whole. Especially, free fatty acid contents were higher than other lipids. After UV irradiation, lipid contents were decreased. These patterns were shown in all human populations. Asian hair has more integral hair lipid than European or African hair. After UV irradiation, European and African hair samples exhibited more damage because they have less integral hair lipids. However, Asian hair samples have less damage.ConclusionWe conclude that integral hair lipid may protect the hair against the UV light.
Human hairs experience damage and restoration processes consistently because of various external and internal factors. To analyze degrees of hair damage, morphological studies based on electron microscopy (EM), and biochemical studies based on protein and lipid analysis have been proposed and are widely used. Among them, morphological analysis through EM is a fundamental method in understanding the degree of damage and restoration. EM has been very useful in assessing extrinsic and intrinsic damage of hair and various pathological alopecias and also in estimating the efficacy of various kinds of products related to hair care. However, morphological studies have some limitations because they have been described using varying terms and subjective descriptions by different researchers. To establish an objective classification of damaged hair using uniform terms and standardizations. We analyzed over 2000 scanning electron microscopic and transmission electron microscopic findings of normal and of various kinds of damaged hairs to develop a standard grading system for the damaged hairs. After reviewing the results of the electron microscopic pictures, we proposed a standard grading system based on scanning electron microscope and transmission electron microscope. We developed and proposed an easy, objective, and useful standard grading system of damaged hairs.
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