Found just below the skin's surface, the hair root is encased by a follicle. At the bottom of the follicle is the dermal papilla, which is nourished by the bloodstream. Composed of a group of fibroblast cells, the dermal papilla instructs the follicle to make hair fiber.
Each hair grows in cycles that take place in three stages. The Anagen, or growth phase, can range from two to six years, during which a hair grows about 10 cm per year. The Catagen, or transitional phase, occurs at the end of the growth phase. During this phase, the follicle withers and the dermal papilla falls off. During the Telogen, or resting phase, the hair remains attached to the follicle but does not grow.
Two melanin pigments, eumelanin and pheomelanin, give hair its color. Although each hair contains less than one percent of melanin, there is a wide range of natural variation. Black or brown hair results from the predominance of eumelanin in the cortex, while blonde or red hair contains more pheomelanin.