Structure
There are differences across ethnicity in the structure, density, and growth rate of hair. With regards to structure, all human hair has the same basic chemical composition in terms of keratin protein content. However, Franbourg et al. have found that Black hair may differ in the distribution of lipids throughout the hair shaft. Afro-texture hair was not as densely concentrated as other phenotypes. Specifically, the average density of Afro-textured hair was found to be approximately 190 hairs per square centimeter. This was significantly lower than that of Caucasian hair, which, on average, produces approximately 227 hairs per square centimeter.
Further, Loussourarn found that Afro-textured hair grows at an average rate of approximately 256 micrometers per day, while Caucasian hair grows at approximately 396 micrometers per day. In addition, due to a phenomenon called 'shrinkage', Afro-textured hair that is a given length when stretched straight can appear much shorter when allowed to naturally coil upon itself. Shrinkage is most evident when Afro-hair is (or has recently been) wet. Haven|publisher=Thenaturalhaven.blogspot.com|accessdate=2012-06-20}}
A hair's shape is never completely circular. The cross-section of a hair is an ellipse which can tend towards a circle or be distinctly flattened. Asiatic heads of straight hair are formed from almost-round hairs and Caucasian hair's cross sections form oval shapes. Afro-textured hair has a flattened cross-section and is finer, and its ringlets can form tight circles with diameters of only a few millimeters. Asiatic hair can be observed as being the most common while Afro-textured hair is the most uncommon.
Afro-textured hair strands can also possess "torsion twists", where the hair strand turns around itself. This can be felt as a permanent crimp. The simplest analogy would be the wringing of a cloth where you turn one side clockwise and the other anti-clockwise. These torsion twists may prevent the hair strands from "clumping" together into curls, instead separating them and allowing them to have a fluffier, more undefined look.
Read more about this topic: Afro-textured Hair
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