Hair is one of the defining characteristics of mammals, specifically humans. Part of the integumentary system (the body system that protects us from damage), hair grows from the dermal layer of skin through the epidermis and protrudes away from the body to form a protective layer. Human hair has a number of important biological uses.
Hair Protects Against UV Rays and Debris
The hair on our heads protects our abnormally large brains (in relation to other mammals) from the harmful effects of the sun’s ultraviolet (UV) rays. While some believe that the hair shaft acts like fiber optics, thereby facilitating the passage of UV light, the natural snags in hair diffuse the harmful rays. In addition, our eyebrows protect our eyes from UV light and deflect debris.
Hair Helps Us Detect Harmful Substances
Because hair retains concentrations of heavy metals (lead, mercury, arsenic and the like), it can be used when testing for these harmful metals in the human body. The concentration of these substances in human hair is, in fact, ten times more than that found in the urine or blood.
Hair Protects Against Excessive Heat
Hair helps to keep the head cool. Human hair on the scalp provides shade from the sun. The low density of Afro-hair, for instance, along with its coiled structure, helps to circulate air around the scalp while shutting out ambient heat.
Hair Insulates Our Bodies
In cold weather, hair helps to prevent a drop in body temperature. Because we are literally covered in hair, the skin has an easier time retaining heat when temperatures drop. Millions of hairs act as insulators by trapping body heat and keeping it close to the skin.
Hair Helps Us Maintain Equilibrium
Hair cells are instrumental in helping us keep our sense of equilibrium (orientation with respect to gravity). When our bodies accelerate, decelerate, spin or fall, sensory hair cells are prompted by a sequence of events within the ear to release transmitter chemicals, which in turn stimulate sensory neurons to give us our orientation.