The skin is the envelope of the human body and its main protector. It separates the body from the outside world while allowing it to be in contact with it. The skin is the body's largest organ and the centre of touch and sensitivity. It is essential to respect its structure and its functions (thermo-regulation, skin breathing, ...), as its well being is vital for us.
The skin is made up of three definitive layers (see image)
The Epidermis is the visible and superficial part of the skin and is formed from 6 layers. (see illustration)
The Dermis lies between the Subcutis and the Epidermis and is a fibrous tissue made up of collagen fibres (which maintain moisture levels and add strength to the skin) and elastin fibres (which give to the skin its suppleness and its elasticity). With age, these fibres deplete and fine lines start to appear. The Dermis is also a complicated network of sebaceous and sudoriferous glands, blood capillaries, nerve endings and corpuscules (for example tactile corpuscules).
The Subcutis is the deepest part, forming a layer of adipose tissue (a "fatty cushion") which allows the underlying organs and muscles, which the skin covers, to move freely. It also acts as an effective shield against damages due to surface knocks and blows. It is interspersed with bundles of nerves and blood vessels.
The epidermal cells arise from the deepest layer and multiply themselves: mitosis. They are active (nucleus) and moist. Some contain melanin: the melanocytes (skin pigmentation), some others contain keratin (protein): the keratinocytes.These gradually push upwards to form the visible layer.
As they move upwards, the keratinocytes lose their plumpness and moisture. They become scaley, flatter and harder: cornification process.
These lifeless and keratin filled cells are now perfect for their final role: protecting your skin against external damage. Finally the lifeless keratinocytes loosen themselves and continuously exfoliate: desquamation process.
These keratin debris, the secretions of sebaceous and sudoriferous glands and the epidermal lipids compose the "protective mantle" (hydrolipidic mantle) of skin.
The perpetual cycle of continual cell renewal takes between 15 and 30 days, depending on age and personal metabolism. The older you are the slower the process, which causes skin to dehydrate and fine lines to become more visible.