The Biology and Genetics of Curly Hair

Abstract

Hair fibers show wide diversity across and within all human populations suggesting that hair fiber form and colour has been subject to much adaptive pressure over thousands of years. All human hair fibers typically have the same basic structure. However, the three dimensional shape of the entire fiber varies considerably depending on ethnicity and geography, with examples from very straight hair with no rotational turn about the long axis, to the tightly sprung coils of African races. The creation of the highly complex biomaterials in hair follicle and how these confer mechanical functions on the fibre so formed is a topic that remains relatively unexplained thus far. We review the current understanding on how hair fibers are formed into a non-linear coiled form and which genetic and biological factors are thought to be responsible for hair shape. We report on a new GWAS study comparing low and high curl individuals in South Africa, revealing strong links to polymorphic variation in trichohyalin, a copper transporter protein CUTC and the inner root sheath component keratin 74. This builds onto the growing knowledge base describing the control of curly hair formation.

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