Current technology and advances in transepidermal water loss sensors

The skin is an organ with twofold functionality. It prevents the loss of internal fluids and provides a protective barrier against exogenous agents that may damage or alter the biological functions of an organism. Nevertheless, skin is permeable to water molecules through a passive diffusion process called transepidermal water loss (TEWL), which is not to be confused with sensible perspiration as it excludes the excretions of sweat glands. However, in the literature, the same terminology often refers to the total amount of water loss through the skin. TEWL mainly depends on the external environment relative humidity and temperature, and on the thickness and integrity of the stratum corneum, the uppermost layer of epidermis [1]. Epidermis is the outermost stratum of the skin and is composed of four layers, except in palms and soles where there is a fifth layer called the stratum lucidum. Figure 4.1 shows the epidermis and the main tasks of the stratum corneum [2].