Hair is a filament-like structure that grows from follicles (pronounced: fol-LEKS). Hair is primarily composed of proteins, including alpha-keratin. Hair is one of the most defining features of mammals. The entire surface of the body, except for areas of glabrous skin, contains follicles that produce thick terminal hair and fine vellus hair.
A strand of hair begins at the bottom of the hair follicle, called the papilla, which gets nourishment from a blood vessel that runs underneath it. Cells in the papilla multiply and then harden, a process called keratinization. They are then pushed up through the follicle and through the skin’s surface as a strand of hair.
Each follicle is attached to a sebaceous gland that makes lipid-rich oil to keep your hair and scalp healthy. Hair follicles also have a nerve supply that helps guide the hair growth process.
Hair has many functions, including providing insulation and protecting the skin from dust and other small particles. It can even help reduce the amount of heat that enters your body, which is especially important if you spend a lot of time in cold environments. Hair in the nose and ears protects them from grit and other particles that could scratch or damage your sensitive skin. And the hair that covers the head keeps sweat from pooling on the neck and face.
Most of us think of hair as something that’s either straight or curly, long or short, thick or thin, dark or light in color. But it is actually far more complex than that, with multiple layers and chemical bonds.
The outermost layer of a hair is the cuticle, which is made from protein. Then comes the cortex, which is a bundle of cells that are densely packed together and surrounded by an intercellular cement. The cortex contains bundles of keratin fibers that have long chains of amino acids, which are responsible for the hair’s strength and elasticity. It is also the location of melanocytes (pronounced: melan-oh-KY-tihz), specialized cells that make the pigments that give your hair its color.
Then we have the medulla, which is located between the cuticle and the cortex. It is the smallest part of the hair, which provides support and strength. Finally, there is the dermis, which is where the follicles sit and where the actual hair growth takes place.