White dots: the in-vitro generation of trichorrhexis nodosa and its comparison in different hair types

Trichorrhexis nodosa (TN) is a common hair disorder in which small defects, often called "white dots", develop along the hair shaft, leading to degradation in the hair's texture and appearance and, in some cases, significant hair loss. The condition is well documented in the clinical literature but until now there has been no laboratory test able to simulate the condition in such a way as to distinguish between healthy hair and that of TN sufferers. Following the only previous work in the area (Owens and Chernosky, 1966) we developed equipment which was able to generate the characteristic white-dot features of TN by subjecting hair samples to an abrasive action between rubber plates. Hair from a subject who suffered from TN was found to generate these features in fewer rubbing cycles than hair from two healthy subjects. TN also formed readily in hair from a subject suffering from split ends, and in this case the white dots were associated with longitudinal splits. Scanning electron microscope studies showed that the features generated in this test strongly resemble those from natural TN and allowed us to describe their initiation and development up to hair strand fracture. White dots were also generated using a different type of test, the moving loop fatigue test, which we have used previously to generate splits in hair strands. These findings support the hypothesis that white dots are created essentially by mechanical means, as a result of high localised stresses when two hair strands are pressed together and bend over each other. This work, though preliminary in nature and conducted on a limited set of subjects, paves the way for improved clinical diagnosis of TN and a better understanding of its causes.