Ultrasound shear wave propagation in Caucasian hair.

Background : The aspect of hair depends on the spatial organization of the hair shafts and on their chemical, physical and structural integrity. Some genetic disorders and exogenous influences may affect it. Aims : In vivo objective assessments are welcome in order to compare the consequences of hair damages and to assess the kinetics of the changes occurring in time after damaging or attempting to repair the hair structure. Method : Ultrasound shear wave propagation measured on hair is introduced as an objective non-invasive method with in vitro and in vivo applications. Results : With multiple measurements made on the scalp of 72 Caucasians, hair felting following damage appeared to be associated with an increase in the coefficient of variation of the shear wave velocity measurements. Maximum hydration of hair locks increased the shear wave velocity in vitro and decreased the intraindividual range of data. The relevance of the method and reproducibility of data was influenced by the experimentalist skill. Conclusion : Ultrasound shear wave propagation on hair is influenced by the physical integrity of the hair shafts and on their three-dimensional arrangement.