Hair is a thin and flexible structure that grows from the skin of every mammal. Like horns and nails, it is made mainly of a protein called keratin. Each hair consists of a shaft and a root. The shaft sticks out of the skin’s surface, while the root lies beneath in a hole (called a follicle) in the dermis layer of your skin. The follicle has blood vessels that supply it with nutrients, and new cells grow inside and push out older ones as your hair grows.
Hair has many functions, including thermoregulation and protection from the sun. It also provides a sense of touch and is an important part of communication in humans. It helps us recognize other people, as well as protects the scalp against bacterial infections. In addition, the hair around the eyes (eyelashes) defends the eyes from dust particles and stains.
There are many things that influence how long your hair grows – genetics, of course, plays a big role, but so does nutrition. When your body is not getting enough nutrients, your hair can become brittle and slow to grow. Your hormones also play a role in how fast and how long your hair grows. Estrogen, for example, promotes healthy growth of hair, but when estrogen levels drop — for instance during menopause — the rate of hair growth decreases.
The hair shaft, the part that is visible above your scalp, is made up of multi-layered keratinized (dead) flat cells that are arranged in rope-like filaments. It has a sheen and is fairly strong compared to the rest of your skin. Hair color is determined by melanin pigments that are deposited in the cortex of the hair fiber.
Hair is a complex structure and it is difficult to know exactly when it evolved in the common ancestor of mammals. However, it is believed that body hair acquired by the basal synapsids of crocodiles and other reptiles at a time about 300 million years ago.
The structure of your hair is determined by a series of layers, which are called the cuticle, cortex and medulla. The cuticle is the outermost layer and it consists of tiny scales that overlap each other. It gives your hair its silky texture and is responsible for protecting the inner structures of the cortex and medulla. This protective layer is a natural barrier that shields your hair from the harsh elements of our environment and protects it against damage and stress.