**2. Functions of hair**

Also known as "fur" in animals, hair is a defining characteristic of mammals. Besides its important thermoregulatory function, it also has a camouflage purpose and offers protection. In animals, hair follicles can modify their type and density during seasonal coat changes [1]. It is noted that in some species, hair provides sensory and defensive functions, while in others it is used for signaling and communication [2, 3].

Although human hair has lost its main thermoregulatory function, on the scalp, it preserves a heat insulation and cooling purpose, by evaporating sweat from soaked hair [4–6]. It also acts as a sunscreen, offering the skin protection against ultra-violet radiation [7, 8].
