Hair Basics
Hair provides a number of different benefits, depending on the location. Hair on the head helps to keep the body warm. Hair in the nose filters out dust and small particles. Eyelashes helps protect the eyes from particles. Regardless of the location, a hair consists of a shaft and a root. The shaft extends from the surface of the skin. The root resides below the surface of the skin and ends in a bulb. The bulb sits in a pit that is similar to a sac and is called a follicle. Hair grows longer from the growth that occurs in the follicle.
The Papilla
At the bottom of the follicle, there is a structure called the papilla. An artery feeds nourishment via the bloodstream to the papilla. Growth occurs from the multiplication of cells in the root of the hair. The reproducing cells produce keratin to strengthen the structure of the hair. As the cells reproduce, they are pushed up through the skin as a hair.
Keratinization
As new cells grow at the base of the root, they form a shaft as part of the hair. The production of new cells pushes the shaft up through the skin. Once exposed to air, the cells produce keratin in a process called keratinization. As this process is going on, the hair cells die. The combination of dead hair cells and keratin is the hair shaft, and the shaft will continue to extend farther beyond the surface of the skin as new cells form in the follicle.
Life Cycle
According to The Nemours Foundation, hair grows at about one-quarter of an inch per month. It will continue to grow as cells reproduce at the base of the root for up to six years. The length of time that growth occurs in the follicle can vary between two to six years. At the end of the growth period, the hair falls out, and new hair begins to grow.
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