Hair
Why Do People Have Hair?
Hair grows all over the outside of our bodies, except on the palms of the hands, soles of the feet, and lips. It also grows in the nose, ears, and around the eyes.
Hair does a few different jobs depending on where it’s located:
- Hair on the head and body helps keep us warm.
- Eyelashes help keep dust and other particles out of the eyes.
- Eyebrows protect the eyes from sweat and other liquids (like water spraying from a shower). They also give some protection from sunlight.
- Hairs inside the nose filter out dust, pollen, and other irritating particles.
What Is Hair?
Hairs are thin strands of hardened protein packed into layers. The hard outer layer you see is called the cuticle (KYOO-tih-kul). It protects the two softer inside layers, the cortex (KOR-teks) and the medulla (meh-DUL-uh).
Each hair grows out of a follicle (FAHL-ih-kul), which is a sac-like pit in the skin. At the base of the follicle is the papilla (puh-PILL-uh). This is where the actual hair growth happens.
The root of the hair is the soft bulb at its base. The hair shaft is the part that sticks out from the surface of the skin.
An oil gland, called a sebaceous (sih-BAY-shiss) gland, is attached to a follicle. Oil made in these glands helps keep hair and skin from getting too dry.
How Does Hair Grow?
A strand of hair grows from the bottom of each follicle, at the papilla. The papilla gets nutrients from a blood vessel that runs underneath it. New hair cells form, grow, then die and harden. The hardening is called keratinization (kair-eh-tih-neh-ZAY-shen).
New cells continue to form from underneath and push the hardened cells up the follicle and through the skin's surface as a shaft of hair.
What Gives Hair Its Color and Texture?
Hair color comes from a pigment called melanin (MEL-eh-nen). There are two kinds of melanin in hair— eumelanin (yoo-MEL-eh-nen) and pheomelanin (fee-eh-MEL-eh-nen). The amount you have of each kind determines your hair color.
People with:
- lots of eumelanin have darker (brown or black) hair
- lots of pheomelanin and not much eumelanin have red hair
- small amounts of both eumelanin and pheomelanin have blond hair
Older people often have gray or white hair because their hair follicles can’t make melanin as easily as when they were younger.
Hair texture depends on the shape of the follicles. Some hair follicles produce curly hair. Other follicles send out straight hair. Some follicles make thicker strands of hair while others make thinner strands.