One of the main functions of skin is to act as a protective barrier against the external environment. Both, at aesthetic and functional level, the proper hydration of the skin is essential to protect from harmful external agents, or to act as a barrier against mechanical damage. An oscillating percentage between 10% and 20% will result in an elastic, flexible and firm skin. This percentage will vary depending on internal factors (genetics, ageing, hormonal factors or different diseases), or external factors (diet, proper hydration, sun, wind and pollution).