Long Haired Girl

Each strand of hair is made up of the medulla, cortex, and cuticle. The innermost region, the medulla, is not always present and is an open, unstructured region. The highly structured and organized cortex, or middle layer of the hair, is the primary source of mechanical strength and water uptake. The cortex contains melanin, which colors the fiber based on the number, distribution and types of melanin granules. The shape of the follicle determines the shape of the cortex, and the shape of the fiber is related to how straight or curly the hair is. Asian hair typically has a round fiber and is quite straight. Oval and irregularly-shaped fibers are generally more wavy or even curly. The cuticle is the outer covering. Its complex structure slides as the hair swells and is covered with a single molecular layer of lipid that makes the hair repel water. The diameter of human hair varies from 17 to 180 µm (0.00067 to 0.0071 in).
Hair pigment
All natural hair colors are the result of two types of hair pigment. Both these pigments are types of melanin, produced inside the hair follicle and packed into granules found in the fibres. Eumelanin is the dominant pigment in dark-blond, brown, and black hair, while pheomelanin is dominant in red hair. Blond hair is the result of having little pigmentation in the hair strand. Gray hair occurs when melanin decreases or disappears.