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From the visible to the invisible: understanding skin ageing.

From the visible to the invisible: understanding skin ageing.

Skin ageing is a physiological process, and therefore natural. However, in the presence of certain factors, this ageing process can accelerate. Discover here what the triggering mechanisms of this acceleration are.

Signs of skin ageing.

The skin is the most extensive organ of the human body. It forms a protective envelope of over 2m2 in adulthood. This strategic location makes the skin highly exposed to external factors, primarily to UV rays, which are responsible for photo-induced ageing. We can therefore distinguish:

  • The chronological ageing, inevitable, under genetic and hormonal influence;

  • Photo-induced ageing, or photo-ageing, caused by the sun and other environmental factors (smoking, pollution...).

Photo-ageing is entirely separate from the normal ageing of the skin, and is an additional factor. The mechanisms of skin ageing include the harmful effects of oxidation reactions, DNA damage, and hormonal changes.

Gradually, the cells of the epidermis renew less quickly and the activity of the sebaceous glands decreases, leaving the skin drier and more vulnerable. Wrinkles are the most visible characteristic of skin ageing. Other factors impact the age estimation of a face: the skin is less taut, less firm, brown spots (also known as age spots) appear in areas that have been overexposed to the sun. The face becomes hollow and dark circles form.

What happens at the tissue level?

Like any organ, the skin becomes less efficient over the years. The tissues become looser and less resistant to shocks. Circulation slows down, the skin thins and the subcutaneous fat sags. Moreover, it dehydrates and dries out.

What happens at the cellular level?

Various types of cells make up the skin:

  • the fibroblasts, which produce the skin's support fibres (elastin and collagen) and hyaluronic acid, a molecule that plumps the skin.

  • the keratinocytes, which duplicate at full speed in order to generate the corneal layer and produce a small amount of hyaluronic acid.

  • the sebocyteswhich constitute the sebaceous glands that produce sebum

  • the melanocytes, which synthesise the pigment and give the skin its colour

Every day, cells die and are renewed. Over the years, these cells renew at a slower pace, their quantity decreases, and consequently, they become less efficient. As a result, we observe a reduction in the synthesis of elastin, collagen, hyaluronic acid, and sebum. The melanocytes, on the other hand, become deregulated, and the production of pigments then concentrates in certain areas.

What happens at the molecular level?

The origin of all the above elements comes from the molecular level. Indeed, skin ageing is also observed at the molecular level: proteins, DNA, etc... Over time, the terminal part of the chromosomes (telomere) is no longer well replicated. These, which aim to protect our genetic heritage, gradually decrease until they disappear, which corresponds to the death of the cell and a decrease in the number of cells present in the skin. Still at the nanometre scale, we also observe oxidation phenomena that alter the different components of the skin, leading for example to the fragmentation of collagen and elastin fibres.

Sources:

TOBIN D. J. Introduction au vieillissement cutané. Journal de la viabilité des tissus (2017).

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