Hair Ethnicity 196 the inner root sheath similar to squeezing a water hose near the base, which would produce curvature and ellipticity in the hose.15 In the work reported by Thibaut et al., they found expression of (alpha) smooth muscle actin [(alpha)SMA] associated with the ORS on the concave side of the follicle, which they hypothesize is indicative of a mechanical stress. A third theory suggests that the bilateral distribution of cortical cells forces different parts of the hair to grow at different rates. Munro and Carnaby theorized that the ortho- cortical cells seem to have fused or interlaced microfibrils that are not parallel, suggesting that they are less elastic than the parallel arrangement found in the para-cortical cells and thus stretch less during the initial growth phase, causing the asymmetry that we observe as curl.16 Along with degree of curliness, hair length is controlled biologically, but unlike curl it is directly regulated by growth rate. Hair growth parameters that are inclusive of growth rate, density and telogen count were studied and published over the last five decades.17 These studies varied in methods used and number of subjects studied, but very few compared the parameters for hair from different origins. The methods used to study these parameters have evolved from visual observation and physical plucking to photo and video tricograms that allow the data for all three parameters to be measured from a single sampling. In one of the most comprehensive comparative studies, Loussouarn measured Figure 1 Macroscopic differences between African and Caucasian hair biopsies: (a) Observation of retrocurvature in the African biopsy (b) Curly African hair after microdisection (c) Observation of Caucasian biopsy (d) straight hair after microdisection. A C D B