With a weight of about 4 kg and a surface of about 1.8 m2, the skin is the widest organ of the organism: Its constitution is approximately the same at qualitative level and on the wholebbody. However, it undergoes notable variations especially concerning its thickness, its components, and above all, the way and variety of implantation of the skin appendices. These variations enable the skin to have a perfect functional adaptation.
In addition to its main protective part, the skin also ensures numerous other essential
functions such as permeation, metabolism, and thermoregulation and actively contributes to the sensorial function. This structural and functional diversity is influenced by intrinsic factors related to subjects, their ethnic group, their age, and their physiological, psychological, and pathological state and by extrinsic factors related to the immediate environment such as the dryness level, sun exposure, temperature, and wind.