This enables bidirectional bending stiffness, bending most easily in the direction of the flattened axis. Curly hairs have an elliptical or вЂњDвЂќ shape in cross section.

The distribution of forms of curly hair is shown in Figure 1 and a closer inspection reveals that curly hair fibres are rarely a true coil but exhibit heterogeneity in the direction of the curl in all but the mildest cases. The basic structure of hair-a cuticle, cortex and medulla (in some)-does not reveal how these structures are built by the hair follicle or shaped into the curly fibre, suggesting there is a level of вЂњfine controlвЂќ on the process of hair fibre formation by the hair follicle. This builds onto the growing knowledge base describing the control of curly hair formation.

We report on a new GWAS 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. We review the current understanding on how hair fibres are formed into a nonlinear coiled form and which genetic and biological factors are thought to be responsible for hair shape. 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. However, the three-dimensional shape of the entire fibre 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. All human hair fibres typically have the same basic structure. Hair fibres show wide diversity across and within all human populations, suggesting that hair fibre form and colour have been subject to much adaptive pressure over thousands of years.

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