Hair has a significant physical, psychological and social impact on an individual's daily life and well being. Understanding the basic structure and the factors that affect hair fiber integrity leads to better handling and care of our hair.
Hair is a slowly renewable protein fiber which grows at a rate of about 1 cm per month. Once hair emerges from the scalp, it is a non living matter.' From the scalp exit point to the distal portion of the hair strand, any injury to the hair structure is irreversible. Subjecting the hair fiber to the least amount of dailytrauma helps to minimize any damage to the hair fiber.
Hair fiber is mainly keratin protein and a small amount of lipid and other components. It is made up of an inner cortex, medulla and an external cuticle layer. The hair cuticle is made up of overlapping cell layers (approximately 5-10 layers) which covers the entirehair fiber. Each cuticular cell has inner layers (A layer and the endocuticle), outer sublamellar structures and an outer membrane, containing lipids mainly 18-methyl eicosanoic acid which imparts a hydrophobic nature to the cuticle.' The condition of the cuticle mainly determines the cosmetic appearance of the hair and being the most external layer, is the part of the hair most vulnerable to the effects of daily grooming, cosmetic treatments and the environment.
The cortex has a winded helical configuration of long microfibers linked to each other to form larger structures which gives the hair its tensile strength and elasticity." The inner location of the cortex makes it less prone to damage thus injury to the cortex signifies more severe damage to the outer cuticles allowing extension to the inner cortex. The medulla is the innermost cylindrical part of the hair fiber whose function is not as clear as the other two structures.