Hair Shafts

L. Rudnicka et al. (eds.), Atlas of Trichoscopy, DOI 10.1007/978-1-4471-4486-1_2, © Springer-Verlag London 2012 Most hairs viewed on trichoscopy are normal terminal hairs that are more than 55 m m wide and are uniform in thickness and color [ 1, 2 ] . Hair shaft thickness may be roughly estimated with a handheld dermoscope (thin, normal, thick). Many videodermoscopes include software allowing a detailed assessment of hair shaft thickness in micrometers. Although precise measurement of hair shaft thickness is not essential for diagnosis, it may be useful for monitoring treatment ef fi cacy and in clinical trials. In normal hair shafts, trichoscopy allows visualization of the medulla, which is classi fi ed as continuous, interrupted, fragmented, or absent [ 3 ] . The trichoscopic impression of the “fragmented” medulla is in fact a thick medulla separated by a thin medulla, which is not visible on trichoscopy. The thickness or presence of a medulla is believed to have no in fl uence on hair shaft properties [ 3 ] . Up to about 10 % of normal human scalp hairs are vellus hairs, de fi ned as hypopigmented, nonmedullated hairs less than 30 m m thick and less than 2–3 mm long [ 1, 2 ] . An increased proportion of vellus hairs is characteristic of male and female androgenetic alopecia, in which vellus hairs replace terminal ones during the process of hair follicle miniaturization [ 4, 5 ] . A high percentage of vellus and intermediate hairs contributes to increased hair shaft thickness heterogeneity, a hallmark of androgenetic alopecia [ 4, 6 ] . Vellus hairs must be differentiated from new, regrowing hairs, which are short and thin but differ from vellus hairs by not being hypopigmented and by their fi rm appearance and pointed end. Various hair shaft structure abnormalities may be evaluated by trichoscopy. Exclamation mark hairs are characteristic of Abstract Normal hair shafts are uniform in thickness and color. Trichoscopy allows detection of several hair shaft abnormalities, including various types of fractured hairs, hairs with narrowings, hairs with node-like structures, twisted or curled hairs, hairs with bands, and short hairs. In this chapter, we propose a classi fi cation of hair shaft abnormalities that may be detected by trichoscopy.