The skin, an organ in itself

Constantly renewed, the skin is much more than just an envelope. It is the heaviest living organ (3 to 4 kg) and the most extensive in the human body (1.5 to 2 m²). In permanent relation with the other organs, the skin may reveal dysfunctions or pathologies other than cutaneous.

The skin has 3 basic roles:

Protection

It protects the body from mechanical, physical, chemical or microbial attack from the outside environment, among others through immunological and cell mechanisms and its impermeability, strength and flexibility.

Transmission

It is used to transmit information between the body and the outside world through its many nerve endings which receive tactile, thermal and pain stimuli.

Echanges

It is the site of multiple exchanges between the body and the outside environment. It is involved in complex mechanisms such as body temperature regulation (by eliminating heat and evaporating the sweat secreted by sweat glands as well as eliminating harmful substances) and synthesis of vitamin D which is essential to bone growth.

The skin consists of three separate superposed layers:

The epidermis, upper stratum of the skin, is a tissue essentially composed of keratinocytes, cells which, as they age, become charged with a strong, impermeable substance: keratin (which explains the role of skin protection). The epidermis also contains melanocytes (cells which provide natural protection against the sun's rays and are responsible for the skin's pigmentation) and Langerhans cells which are part of the immune system. The epidermis is organized in four layers of cells: the basal layer (the deepest), the mucosal layer, the granular layer and the horny layer (the top layer).

The dermisspan> is a connective tissue of variable thickness which contains blood vessels, many immune cells, sweat glands, pilo-sebaceous follicles, sensory receptors which react to pressure or temperature, and pain-sensitive nerve endings. The main constituents of the dermis are collagen and elastin fibres, ensuring that the skin remains strong, providing support, flexibility and elasticity.

The hypodermis, located under the dermis, is a fatty tissue, more or less abundant according to individuals and parts of the body. It forms an important energy store for the body.