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The structure of the skin
The skin is the most extensive organ in our bodies. It is composed of three superimposed layers :

Epidermis : the outermost (superficial) layer of the skin. Its thickness varies. The epidermis has no blood supply. Surface cells (horny layer) are shed through desquamation. The cells below move up to renew the layer. Melanocytes and Langerhans cells are located in the epidermis..

Dermis is a thick, elastic layer which constitutes the skin’s supporting tissue. It contains collagen and elastin fibres. The main cells in this layer are fibroblasts, which synthesise collagen and elastin fibres, glycosaminoglycans and structural glycoproteins. The dermis contains the skin’s vascular network, nerve fibres and sensory receptors. It is also home to sebaceous and sweat glands, as well as hair follicles.

The epidermis and dermis are connected by the basal layer, where keratinocytes form.

The hypoderm consisting of adipose tissue made of adipocytes (fat cells), is the lowermost layer of the skin. It is the body’s energy storage. Fat can be stored here as triglycerides or released as fatty acids and glycerol. The hypoderm acts as padding for the body and protects it from the cold.

Functions of the healthy skin

• Protection against external factors : physical, chemicals, microbial, ultraviolet and heat. The skin can also cicatrise to close wounds.
• Thermoregulation : ts vascular system and sweat glands help the body maintain a temperature of 37°C.
• Touch : the skin takes in a wide range of information from the outside world (heat, cold, etc.). Nerves are responsible for the sense of touch. The skin also provides insight into our mood and emotions.
• Metabolism : it synthesises vitamin D (helping preventing rickets) using ultraviolet radiation.
• Regulation : the skin preserves its water content.

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The two major types of skin ageing

Intrinsic ageing, is inevitable and its characteristic changes affect protected areas.

Extrinsic ageing caused by external factors: the environment, pollution, smoking and ultraviolet radiation. This type of ageing affects exposed areas by definition. It can be mitigated by a healthy lifestyle, watchful care from age 30 and the use of the appropriate products.

Factors behind skin ageing

Ageing is the consequence of seven factors. As a result, the visible clinical expression of ageing depends on age and each person’s genetic predisposition, which determine chronological age when combined. Other factors influence the signs of ageing. These seven factors are :

• Time,
• Genes,
• Solar radiation (ultraviolet and infrared)
• Behaviour: smoking, drinking, diets, drugs, etc…
• Diseases
• Hormonal changes
• Trauma and weight.

Visible signs of intrinsic ageing :

• Atrophied skin layers (epidermis, dermis and hypoderm)
• Fragile skin
• Reduced elasticity and firmness, more conspicuous expression lines
• Significant dryness
• Functional changes: impaired cicatrisation, diminished immune and inflammatory response, reduced mechanical and thermoregulatory function,

Visible signs of extrinsic ageing :

• Thicker skin
• Deep wrinkles
• Rough, dry skin
• Loose skin
• Irregular pigmentation and spots
• Appearance of small blood vessels.

The part you cannot see : cellular senescence

Cells divide increasingly slowly until they stop proliferating. This happens, for example, to fibroblasts, key components of the supporting tissue.