Anatomy of hair

Besides understanding silicone, to effectively treat hair an understanding of hair anatomy is also important. Because the study focused on the shaft of hair and nothing sub-dermal, the anatomy of the shaft of hair was primarily investigated. Looking at Figure 3, the shaft is comprised of three distinct regions: the cuticle, cortex and medulla. The cuticle is the thick, protective outer layer of the shaft made of overlapping, flat, keratin structures similar to scales. Within this outer shield lies the cortex, which contains stacked, spindleshaped cells and is where a majority of the fibrous proteins are contained. Near the centre of the fibre lies the medulla which is loosely packed porous regions.2 Hair texture is determined by several bonds – hydrogen bonds, salt bonds and disulfide bonds. Typically, disulfide bonds need a chemical reaction to alter but hydrogen and salt bonds can be manipulated by heat and moisture. It is this ability of moisture to alter these bonds that leads to frizz. Moisture in the air relaxes the salt and hydrogen bonds within the protective cuticle layer allowing moisture to enter the cuticle. When moisture reaches the fibrous region, differential absorption by the proteins causes uneven swelling, creating a frizzy appearance.1


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