Recent research on the molecular biological factors underlying curly hair has demonstrated that the biological factors controlling the processes of keratin formation and regionalized localization of specific types of keratin that are associated with curly hair are represented in all curly hair fibers independent of ethnic types. The biochemical factor promoting curly hair fibers to become ingrown is the selective accumulation of hHa8 keratin on the concave side of the hair fiber which differentiates sooner and more completely than the cortex on the convex side [7].
Insight into the developmental process contributing to asymmetry in cortex demonstrated that delayed differentiation of the inner and outer root sheath on the convex side of the beard fibers is the result of a sustained zone of highly proliferating bulb matrix cells on the convex side of curly hair shafts, which fail to differentiate at the same time as the cells on the concave side. The differential proliferation rates on each side of the follicle results in
the asymmetric spatial and temporal differentiation program [8]. One other risk factor associated with the keratin formation process is the K6hf keratin gene affecting proteins synthesized in the companion layer of the hair follicle which is connected to the inner root sheath. The presence of a malformation in keratins in this region, which is involved in molding the hair shaft, may impact the growth and structure of the hair in a manner predisposing the hair shaft to become coiled and curved during its ascent through the skin and onto the skin surface [9].