title: Normal head-hair length is correlated with its diameter.
abstract: Shed head-hair fibres of young (16-20-year-old), nonalopecic women (n = 25), exhibiting both exogen clubs and anagen tips (EA) were studied. Such fibres are shown, for the first time, to comprise approximately 44% of shed hair and to form a uni-modal, positively skewed distribution with a mean length of 16.7 +/- 4.9 cm, which is also correlated with the length of the haircut. As individual fibres exit the skin in early anagen VI, their major-axis diameters increase rapidly to maxima at about 25% of their total potential length and subsequently decrease to their exogen clubs, at a rate of 1.31% per cm (n = 28). EA diameters are further correlated with their lengths. Maximal and proximal diameters increase by 1.40% per cm and 1.02% per cm increments in fibre lengths, respectively (P < 0.0001 each; n = 14), these changes being also different from each other (P < 0.001). Besides identifying and characterizing a new class of normal hair (EA) which will probably feature prominently in future hair research, this study reveals several other important aspects of hair growth: (i) the classically described concept of hair miniaturization in androgenetic alopecia (AGA) is excessively broad and should therefore be revised; (ii) female AGA need not necessarily require a mechanism for rapid miniaturization as recently proposed; and (iii) the putative large variability of normal hair diameters is significantly overestimated, which further opens the field of hair diameter evaluation as a biological indicator of disease and physiological function.
authors.affiliation: Department of Experimental Medicine and Cancer Research, Faculty of Medicine, Hebrew University, Jerusalem, Israel. nissimov@cc.huji.ac.il
authors.forename: J
authors.initials: J
authors.lastname: Nissimov
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006197:Hair / Q000033:anatomy & histology* / Q000254:growth & development; D006801:Humans; D012016:Reference Values; D012535:Scalp; D013048:Specimen Handling / Q000379:methods