Hair has many functions, including regulating body temperature and protecting the skin and the scalp. Hair also works to extend the body's sensory capabilities.
Hair in both humans and animals serves as a layer of protection against the cold. The hair acts as insulation for the body, especially the scalp.
Hair protects the scalp against harmful ultraviolet rays from the sun. It also provides a layer of cushioning to protect the scalp and skull from trauma.
Hair in both animals and humans enhances the body's sensory abilities. When the hair is moved, even slightly, it sends signals to the brain that the movement has taken place. An example of this is when an insect lands on the arm. Even if the insect is tiny, when it lands on the hair, the person is aware of the movement.