A case of trichorrhexis nodosa developed in winter.

A young Japanese man developed localized trichorrhexis nodosa (LTN) of the scalp hair in the winter season. To investigate the roles of shampoo, severe sunlight exposure and/or mechanical injuries, we performed the following studies. Hair was collected from the patient and from a control. The study was performed in two steps. In the first step, hair was put into shampoo, rinsed with saline water, and then exposed to ultraviolet B (UVB) radiation once a day for one week. In the second step, the hair was similarly treated, but each shaft was bent gently with forceps before UVB exposure. Scanning electron microscopic studies revealed cuticular changes when the hair was treated only with shampoo and UVB. When it was treated with shampoo, UVB, and mechanical bending, the patient's hair developed longitudinal and transverse fractures of the hair shafts, while the control hair showed only partial damage to the hair shaft. On the basis on the above findings, we conclude that mechanical bending may damage the hair shaft.