Abstract: Objective To analyse the cause and pathogenesis of bird's nest hair (BNH) by clinical features, light microscopy(LM), scanning electron microscopy(SEM) examination and trichogram computer image analysis(CIA). Methods The main points of diagnosis and differential diagnosis criteria were found out by analysis of clinical features. According to their bending, the hairs were divided into three groups and examined by LM, SEM and CIA. Results (1)LM: The affected hairs bent and twisted, and some twisted round over 180°with “hairpin like”shape, but the knotting of hairs was not observed. The diameters of hairs varied, some hairs became much thinner. Some fibers splitted at the free end or longitudinally. (2)SEM: There were large quantities of debris and exogenous substances adhering to the surface of the hair shaft. The free edges of cuticules were loosen and fissured. The free end of hairs splitted like a "brush". (3)CIA: There were significant differences between affected and healthy hairs (P<0.05) in the aspects of diameters, bending angle, surface condition, luster, shape, integrity, interval of cuticules and histogram image(P<0.05). Conclusion The results show the abnormality of the surface of hair shaft of BNH.

Key words: Hair diseases, Image processing, computer assisted