General Facts About Hair
Structure of Hairs
• Hair is made up of proteins called as keratins. The hair fiber has three cell layers: an outer cuticle, the cortex (which forms the bulk of the fiber in most hair types) and a variable central medulla
• It is fixed to skin through a tubular structure called as hair follicle. A hair follicle extends from skin surface into the dermis (middle layer of skin).
• The hair follicle is divided into two regions: the upper part consisting of the infundibulum and isthmus and the lower part comprising the hair bulb and suprabulbar region.
• The upper follicle is a relatively constant structure, whereas the lower follicle undergoes repeated episodes of regression and regeneration during the hair cycle.
• Cells from hair bulb give rise to different layers of hair fiber.
• On the scalp, and some other regions of the skin, hair follicles are arranged in groups of three or more follicles known as follicular units.
Hair Cycle :
• Hair follicles undergo a repetitive sequence of growth and rest known as the hair cycle;
It consists of three stages, Anagen, Catagen & Telogen
The period of active hair growth is known as anagen and the duration of this phase is responsible for determining the final length of the hair.
Under normal circumstances 80-90% of hair follicles on the human scalp are in anagen at any one time.