It rests on top of the dermis from which it is separated by the dermal-epidermal junction. Consisting of a stratified structure, its average thickness is 1mm.

4 types of cells are found here:

• The keratinocytes: these form epidermal keratin. As the predominant cell type, they constitute 80% of the cellular population found in the epidermis.
• The melanocytes: these produce melanin, the pigment that provides the skin with its colour and protects it from the sun’s rays.
• The Langerhans cells: acting as veritable gatekeepers, they provide immune defence, particularly in capturing allergens.
• The Merkel cells: originating from nerve cells, they are highly sensitive receptors involved in the sense of touch.

The epidermis is made up of 4 cellular sublayers:

• the basale stratum: the deepest layer of the epidermis. Produces germinative cells known as keratinocytes, melanocytes and Merkel cells.
• the spinous layer
• the granular layer
• the horned layer: the outermost layer of the epidermis. Made up of keratinised cells known as corneocytes and intercellular lipidic cement.

Cell renewal or the keratinisation process

The epidermis is in a constant state of renewal. In the basal layer, the keratinocytes are produced and then divide into two identical cells. One will remain in place and continue to divide, while the other will gradually migrate up to the horned layer – the external and visible part of the epidermis.

This is the differentiation process.

At the end of this migration, the keratinocytes unlodge the corneoctyes (= keratinocyte that has lost its nucleus), which are then shed as squames. This shedding phenomenon known as desquamation is the final stage in the life of an epidermal cell. It takes between 21 and 28 days.

This is cellular renewal.