Chapter 6 197 growth rate, density and ratio of telogen hairs from a worldwide sampling of individuals from 21 countries/regions of origin covering five continents. In all, more than 2,100 men and women were examined. The profiles were determined by the phototriogram method. Irrespective of gender and scalp location, growth rates were determined to range 0.8 cm/month to 1.3 cm/month with an inverse relationship between growth rate and degree of curliness. The lowest rate was observed for curly African hair and the highest was for straight Asian hair. The % telogen hairs ranged 8-14% and the density was between 159-233 hairs/cm however, no relation to the degree of curl was noted for either of the latter parameters. Hair density was dependent upon region of the scalp and varied as follows: vertex occipital temporal. In a smaller study conducted earlier of more than 500 healthy volunteers, hair growth parameters were measured and compared between Asians, Africans and Caucasians.18 Table 1 shows the results from the smaller study. Table 1 Hair growth parameters for African, Asian and Caucasian subjects (mean ± standard deviation) Growth Parameter African Caucasian Asian Density hairs/cm2 161 ± 50 226 ± 73 175 ± 54 % telogen 14 ± 9 12 ± 8 12 ± 7 Growth rate [µ]m/day 280 ± 50 367 ± 56 411 ± 53 The large variability and moderate sample size prevented the author from drawing strong conclusions. However, the African hair tended to grow more slowly and had the lowest density. Hair from Asia had low density and the fastest growth rate, and Caucasian hair had the highest density. It is interesting to note that while these results were reported as a function of ethnic origin, the in vitro follicle studies discussed above indicated a slower growth rate for curved follicles. So the question remains whether the growth parameters are related to ethnic origin or curliness as controlled by the follicle.