How Hair Grows and Functions


Hair is an important feature of human body, both in appearance and in function. It protects the head from the sun’s UV rays and is an insulator against both extremes of hot and cold temperatures. It is also a social signifier of one’s gender, culture and age. A young girl with long blond locks might be a tomboy, while a mature man with short dark hair is likely a business executive or retiree. Hair can be dyed or bleached, and the color reflects the person’s overall health.

The color of the scalp hair is primarily determined by its genetic makeup, but it is also influenced by the oils produced in the glands that line the hair follicles. These oil glands are called the sebaceous glands, and they help to keep the skin and hair healthy. They also contribute to the color of the scalp hair, which comes in many shades of brown, blonde, red, copper, yellow and gray.

Each hair grows from a small hole in the skin, called a follicle. Inside each follicle are stem cells that continuously create new hair in cycles of growth, rest and death. The stem cells surround a bulb of fat, called the dermal papilla, that gets its nutrients from a blood vessel below it. The follicle is attached to a smooth muscle that can make the hair “stand up,” similar to goose bumps in humans and, more visibly, in animals such as grizzly bears with their thick fur. The hair follicle is also connected to nerves that sense any movement in the hair.

As the hair grows, it pushes the hardened cells up through the follicle and out into the outer skin layer, where it becomes visible. This process is called keratinization (kair-tih-neh-ZAYS-hen). The follicle and the hair bulb also have oil glands that produce sebum, an essential oil that helps to keep the hair hydrated.

Although hair is dead keratin, it can still function as a communication tool. In mammals, hair can be a way of expressing emotion through the shape and length of the hair, such as when a lion’s mane curls up or a porcupine quill elongates. In some animals, like hedgehogs and porcupines, the hair can even be modified into hard spines that serve as protection against predators.

As your characters grow, use your hair descriptions to tell a story about them. You can even use it to describe the character’s behavior and actions in a scene, such as how a person moves their hair when they walk. Using all your senses in character descriptions will bring your reader closer to the character and give them a more rounded picture of who they are.