Generally there are four types of shapes of multicultural hair that exist around the world, for example, oriental or Mongolian hair, Caucasian hair, African - descent hair and mixed race wavy hair. The Mongolian or oriental hair is extremely straight, Caucasian hair is not as straight as the Mongolian hair but it is relatively quite straight. On the other side of spectrum, African-descent hair is extremely curly, whereas mixed race wavy hair comes in tremendous varieties because of variation in the degree of ortho cortical cells in hair cortex.
Figure 2.13: Shapes of Mangoloid/Asian, Caucasian, and African-American hair.
One of the ways to compare different hair textures is to compare the radius of the waves in the hair. If the radius of the wave is large then the hair tends to be slightly wavy: as this wave radius turns small, the hair becomes wavier[i]. The other way is to compare the cross section of the hair fibers in terms of their major and minor axis. The ratio of the diameters of major to minor axis determines the ellipticity of the hair fibers as explained under Structure of Hair. It is a well-known fact that as the ellipticity of the hair increases; the curliness of the hair fibers also increases.
The ellipticity of Mongolian or Oriental hair is 1. 20, Caucasian hair is 1.4, and African hair is 1.89 or 1.86, as reported by Kamath et al[ii] and Syed et al[iii]. The ellipticity of curly Afro Brazilian hair exceeds even 1.89 for certain hair fibers. The ellipticity of curly hair changes across the length of the fiber significantly and ranges from 1.00 to 3.25 (Syed et al, 2013)[iv]. Therefore, it proves that African hair is extremely elliptical and it is like a twisted oval rod or ribbon whereas straight Caucasian hair and Mongolian hair have a more cylindrical shape. Figures 2.14 show the fiber ellipticity scan of a fiber 5 centimeters in length for African American hair.
Figure 2.14: The diameter (X and Y axis) scan of an African-American hair fiber is 5 cm is length.
The fiber shows a very high variability in the fiber diameter from point to point along the hair shaft. This type of hair has many stress point along the hair shaft and breaks very easily upon stretching, as shown in the section under fiber break force comparisons.
Caucasian hair fibers show less variability in their diameter, as shown in the 5 cm scan of fiber diameters along the hair shaft, in Figure 2.15.
Figure 2.15: The diameter (X and Y axis) scan of a Caucasian hair fiber, 5 cm is length.
The variability in X and Y axis of the hair fiber diameter is minimum as compare to African American hair fiber. The X and Y axis of the diameter range between 60 to 80 microns. In case the African-American hair (Figure 2.14), the range of the diameter is 60 to 130 microns along with occasional shifting of major and minor axis.
Hair Diameter Variability along the Hair Shaft:
Hair diameter of the three types of hair indicate that Mongolian/Oriental hair has the least variation in the diameter across a single fiber as compared to Caucasian and African hair fibers. African hair fiber is the most irregular in its diameter across a single fiber compared to Caucasian and Mongolian/Oriental hair fibers, as shown in Figure 2.16.
Figure 2.16: The variability in hair ellipticity of various ethnicities along the single hair fiber shaft
African-American hair exhibits the most variation in fiber ellipticity along a single hair fiber as compared to Afro-Brazilian, Hispanic and Caucasian hair.
[i] Nagase, S., Tsuchiya, M., Matsui, T., Shibuichi, S., Tsujimura, H., Satoh, N., Itou, T., Koike, K., & Tsujii, K. (2008). Characterization of curved hair of Japanese women with reference to internal structures and amino acid composition. J. Cosmet. Sci., 59, 317 –332.
[ii] YK Kamath, and S Hornby. (1984). Mechanical and Fractographic Behavior of Negroid Hair. J. Soc. Cosmet Chem, (35): 21 – 43
[iii] AN Syed, A Kuhajda, H Ayoub, K Ahmad, and E Frank (1995). African American Hair: Its physical properties and differences relative to Caucasian hair, Cos & Toil, 110: 46.
[iv] AN Syed, TN Ventura, and MN Syed. (2013). Hair ethnicity and ellipticity: A preliminary study. Cosmet & Toil, 128, (4), 250-259.