​The skin is made up of three superimposed layers:

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–the outer epidermis , made up of cells called keratinocytes;
–the dermis , very thick, made up of connective tissue cells and intercellular substance;
– the hypodermis , which is the superficial fatty layer.

A functionally very important layer of cells separates the epidermis from the dermis. This is the basal layer, made up of a single layer of keratinocytes, rectangular in shape, aligned vertically, and which rest on a fibrous lamina called the basal lamina.

A skin scar is inevitable when the entire thickness of the epidermis, down to the dermis, is damaged or destroyed.
This occurs with any skin incision by the surgeon's scalpel, whatever the cause.

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During a skin trauma , whatever the cause, if the dermis is not affected and it persists at the bottom of the wound of the epidermal ridges, the scarring of the skin will never be the cause of damage. ' a visible scar.

The visible scar on the surface of the skin is caused by the formation of newly formed connective tissue (fibrous cells surrounded by intercellular substance) which I call the scar line.

But its formation is not immediate.

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What happens immediately after a skin suture?

In the hours that follow, there is a mobilization of the cells of the epidermis (keratinocytes) and in particular the cells of the basal layer and the keratinocytes of the various layers of the edges of the wound over 1 to 2 mm in width.

The cells take their final place and fill all the space. The migration is complete.

Nothing moves for 1 to 2 days.

Then, epidermal cell multiplication, also called epithelialization, begins, still from the basal keratinocytes but also from the edges of the wound over 1 to 2 mm.

Cell division, also called cellular mitosis, then begins.

The basal cells differentiate into superficial or corneal cells by passing through the various intermediate stages.
At first, this differentiation is rapid, 4 to 5 days, whereas on normal skin, the basal cells take 14 to 18 days to become horny cells.

It is necessary to specify two very important aspects of epidermization:

–it is continuous: the skin is always renewed, normally, in 15 to 18 days. From month to month, we therefore always have a different skin, although it has the same visual appearance;
– it is infinite  : due to stem cells located in the basal cell layer. Indeed, the keratinocytes of this basal layer are differentiated in two ways:
– either towards the formation of stem cells, in reserve;
– or to the spiny then granular cells up to the stratum corneum.

In 2 to 3 weeks, the scar line is then formed which is due to the presence of these mitoses.

This pink or even red line is a little thick. This stage of hyperplasia remains moderate (little wide and thin scar line) and only lasts 3 months.

Then begins the stage of involution. The scar line improves until the 6th–8th month. The useful, albeit arbitrary, limit for medico-surgical expertise, indications for revision surgery and assessment of the result is therefore set at 12 months.

Two dogmas are thus to be remembered:

–never retouch a scar before the 12th month (except in special cases);
–the aesthetic appearance of a scar can only be judged after the first year following the suture.

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