Keratinocytes from the basal layer (deeper layer) gradually migrate to the surface undergoing different mutations.
They finally lose their nucleus to reach the stage of corneocytes and constitute the stratum corneum. (Upper layer)
Dead cells are naturally evacuated by sweat and sebum. Thus the skin renewal is done naturally in 21 to 28 days
What is the hydrolipidic film?
The surface of the skin is covered with an emulsion of water and fat which forms a hydrolipidic film. Its main function is to form a protective barrier against bacteria and fungi. It also contributes to the suppleness of the skin.
The quantity and the composition of the hydrolipidic film vary according to the parts of the body, but also according to exogenous factors (humidity of the air, season) and endogenous (stress, disease).
It includes, in variable quantities:
- cells residues
-water from the deeper layers of the skin
What is sebum used for?
Sebum is an oily substance secreted by the sebaceous glands attached to the hair follicles.
Sebum secretion participates:
- in maintaining hydration of the epidermis (sebum is part of the hydrolipidic film of the skin)
- to suppleness and softness of the epidermis
- in the balance of the cutaneous bacterial flora.
An excess of sebum can give a shiny appearance to the skin and favor the appearance of blackheads or pimples. On the other hand, the lack of sebum weakens the skin and makes it dry.
The functioning of the sebaceous glands is linked to hormonal activity: the production of sebum is often greater during adolescence or during pregnancy, periods of high hormonal activity.
What is the skin flora?
The hydrolipidic film of the skin is colonized by a microbial flora essential to its protection and to our immune system in general. This flora resides stably on the skin: we speak of resident, permanent or commensal bacterial flora.
It is composed of non-pathogenic organisms.
Its composition varies according to:
- the climate (temperature, humidity, pH)
- the age: the skin of the newborn is devoid of microbial flora. The activity of the sebaceous glands increases at puberty, promoting the proliferation of several bacteria. The skin of very old people being drier, the skin flora is less rich.
- the body region
This medium can also be temporarily colonized by other potentially pathogenic organisms.
What role does sweating play?
Perspiration plays different physiological roles.
It allows thermoregulation of the body: sweating begins when the outside temperature becomes higher than that of the body or when the body temperature rises, for example during sports or in case of fever.
It contributes to the hydration of the epidermis: the hydrolipidic film covering and protecting the epidermis is essentially constituted by sweat and sebum.
It facilitates the adhesion of the palms of the hands and the soles of the feet to different surfaces, allowing the gripping of objects, walking and running while avoiding slipping.
It participates in the expression of emotions, with emotional sweating caused by stress and secreted by the apocrine glands mainly in the forehead, armpits and palms of the hands.
The renewal of skin cells is necessary for the proper functioning of this organ. The hydrolipidic film, the microbiome, the sebum and the perspiration participate in its balance which must be respected by using care appropriate to the skin type.