Hair Ethnicity 204 spectrum, because it’s curly, elliptical in cross-section and relatively thinner with more variability along its length. Caucasian hair is usually in between these two extremes (see Table 3). Table 3 Typical physical characteristics of hair from different ethnic groups. Numeric values are expressed as mean ± confidence interval (CI) at 95%. Ellipticity = maximum/minimum diameter. Cross-sectional Area (µm)2 ± CI Ellipticity ± CI Break Stress (MPa) ± CI Typical Colors Asian (n=173) 5063 ± 179 1.29 ± 0.03 209.7 ± 2.5 Dark-brown, Black Caucasian (n=171) 4079 ± 170 1.41 ± 0.03 202.3 ± 2.2 Blonde, Red, Brown, Dark-brown African American (n=251) 4210 ± 122 1.66 ± 0.02 189.3 ± 2.0 Dark-brown, Black While most are able to understand generalities in geometry and curl from the most commonly compared ethnic groups, as mentioned earlier, the world is much more diverse thus, adjectives such as straight, curly, wavy, frizzy, and wooly that have been used in the past can be confusing and inaccurate because of their subjectivity. In addition, the reference of racial groups can sometimes be an issue which is consistent with dermatologists who have raised concerns about its inadequacy when describing curl in hair.34 This challenge was overcome with the development of a curl classification that uses single fiber measurements to quantify the degree of curl in hair with no reference to race, ethnicity or subjective terminologies.35 Loussouarn et al. studied virgin hair that originated from 22 different countries and the sampling resulted in the characterization of hair from more than 2,400 volunteers.36 The classification objectively measured curl diameter, curl index, number of twists, and number of waves from single fibers and averaged the results from four fibers from each individual’s head. These results were