Hair is a thin, flexible structure that grows from every mammal’s skin. It’s made mainly of a protein called keratin, but it also contains some fatty acids that give it its shine and strength. It has a tensile strength that can stretch farther than steel can before it breaks.
Hair protects animals from cold temperatures and keeps dust and other debris from entering their bodies. Its main function is to help them retain heat and to make their body parts blend in with the environment, but it also helps them feel things that touch their skin. For example, whiskers on an animal’s face are a type of hair that helps the animal sense things like small twigs and branches. People use the fur of sheep, rabbits, mink, foxes, and other mammals to make coats and hats. They also weave it into textiles to make clothes, sheets, blankets, and other soft furnishings.
Each hair grows from a hollow saclike hole in the skin called a follicle. Inside the follicle is a cluster of special cells that can keep growing and regenerating, forming new hairs as old ones fall out. Hair is usually long and thick, but it can be curly or straight or fine and thin. Each type of hair is associated with a specific shape and structure of the follicle that creates it.
The outermost layer of each hair is a tough, shiny covering called the cuticle. The cuticle is composed of overlapping cells that look a bit like fish scales or roof tiles and is responsible for protecting the cortex and medulla of each hair. The cortex is the middle layer that gives the hair its color, texture, and strength. The medulla is the innermost layer, and it stores nutrients that feed the follicle.
Each follicle is attached to a tiny muscle called the arrector pili. When this muscle contracts, it causes the follicle to raise its shaft above the skin’s surface. This is what makes your hair stand up when you comb it or run your fingers through it. The contraction of this muscle also causes the iris of your eye to open and close, and it is one of the ways your eyes communicate with your brain about the world around you.
When you choose to style your hair, the way it looks can be a reflection of your personality and beliefs. Some cultures may have rules about how men and women should wear their hair. In some cases, these rules are based on religious beliefs or cultural norms, but in other instances they are based on social and economic status. For example, a man may not want to cut his hair shorter than his collar, and a woman might not be allowed to grow her hair past her shoulders. Some cultures, however, have no restrictions at all on the length of hair.