The skin and skin ageing
The skin – a vital organ
Indispensable to life, the skin is the largest organ in the human body. Acting as an interface between our organism and the outside world, the skin plays a key role in maintaining body temperature and forming a physical barrier against external aggressions.
The skin – a sensory organ
As the main receptor organ for tactile sensation, the skin transmits vital information to the body about the outside environment.
The skin – a social organ
Captor, emitter and protector, the skin also plays an important social role as our mirror to the world. A real network of emotions, the skin enables the body to transmit information to the outside world about our general state of being - pallor, blushing, etc.
According to one's age, the needs of the skin change and cell regeneration slows down. Both the environment and cell ageing are factors that interfere with the correct functioning of the skin's self-defence and repair systems. The skin becomes thinner, dryer, finely lined and loses its elasticity.
There are two types of ageing involved in the process of cutaneous senescence:
1.Intrinsic chronological ageing
This is the natural ageing process linked to age. It is determined by genetic and hormonal factors. It brings about a progressive degeneration of skin function and structure.
This is ageing caused by:
- repeated sun exposure which causes photo-ageing
- an unhealthy lifestyle (tobacco, alcohol, etc.)
The visible effects of cutaneous ageing are shown by:
- loss of radiance and luminosity
- loss of cutaneous substance = loss of density
- loss of volume (lipoatrophy) = sagging tissue due to lack of tonicity
- cutaneous dryness
- cutaneous hydration slows down due to a drop in the levels of dermal hyaluronic acid
- irregular pigmentation = pigmentation marks
The volume and appearance of the face gradually changes as wrinkles become more pronounced. In time, fine lines turn into permanent wrinkles.
A later but more extreme ageing process occurs in men
Men’s skin generally ages later than women’s skin thanks to its dermis that is coarser and richer in collagen fibres than its female counterpart. Nevertheless once the ageing process does begin, more pronounced and deeper wrinkles can generally be observed.
A journey to the depths of the skin
In order to better understand how the skin works, we invite you to journey through its various cutaneous layers.
Some anatomical information
In an adult weighing approximately 75kg, the skin accounts for around 4kg of that weight and is about 2mm thick depending on the area of the body. It is thicker on the soles of the feet and thinner on the eyelids.
It is made up of:
- three superimposed layers:
- the epidermis: the outermost layer. It protects against external aggressions.
- the dermis: the middle layer. It provides a structurally supporting role.
- the hypodermis: the deepest layer. Largely made up of adipose tissue, it acts as an energy reservoir.
- skin annexes:
- the sweat glands: secrete sweat
- the sebaceous glands: secrete sebum
- appendages of the skin: produce nails and hair
The hydrolipidic film is an emulsion formed on the surface of the skin by sebum and sweat secretions. It helps maintain the skin’s pH balance and forms a natural protective barrier. It also lubricates the skin and maintains its suppleness.
- made up of blood and lymph vessels and nerve endings.
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.
The dermis and protein fibres
The dermis is made up of connective tissue: a gelatinous structure formed from connective fibres, which acts as a liaison and support system between the various tissues and cells. The dermis contains between 20 and 40% of the body's total water content and is between 10 and 40 times thicker than the epidermis.
It consists of 3 layers:
- The papillary dermis
- The reticular dermis
- The deep dermis
In the heart of the dermis, fibroblasts form a tri-dimensional meshing between the different protein fibres which, in turn, provides support for the epidermis and ensures the skin's mechanical properties are maintained. The dermis gives the skin its resistance (Collagen), supports the epidermis and ensures its elasticity (Elastin). It also acts as a water reservoir through the proteoglycan gel.
Highly vascular, it provides the skin with energy and nutriments. In this way, it plays a vital role in the skin's healing and heat regulating processes.
Composition of the Dermis
It is largely made up of:
- Fibroblasts: the predominant cells in the dermis. They synthesize the collagen, elastin and glycoprotein structural fibres. The destruction of these fibres automatically occurs with age. Their numbers drop by half between the ages of 20 and 80.
- Collagen: inelastic fibre and principle structural protein. It is the predominant component of connective tissue and provides support for surrounding tissue. It gives the skin its resilience and firmness. Collagen fibres trap water and thus contribute to the skin’s hydration.
- Elastin: elastic protein fibre that has the ability to stretch and contract thus providing tissues with suppleness and elasticity.
- Extracellular matrix or ground substance in which the connective fibres bathe. It ensures their cohesion and consists of water and proteins = proteoglycane gel (glycoproteins) or mucopolysaccharides from GAG Glycoaminoglycans, the main component of which is hyaluronic acid: sugar-based molecules whose job is to capture water in the dermis.
This is the skin’s energy reserve.
It is composed of loose connective tissue known as white adipose tissue. This, in turn, is made up of cells known as adipocytes that are programmed to store fatty acids. They are clumped together with the papillae adiposae and separated by fibrous walls of collagen and elastin.
Like a mattress, the hypodermis helps give the skin its plasticity, acting as a shock absorber and heat insulator. Its thickness varies depending on the individual and the area of the body in question.
Men’s skin: its differences
The main difference between male and female skin is that they depend on different hormonal systems, which in turn has a fundamental affect on their metabolism.
The following characteristics are also notable:
- Male skin is about 24% thicker than female skin.
- It secretes a thicker and more durable hydrolipidic film.
- The pores are more dilated.
- Its structure is rougher and more resilient.
- It has more hair growth.