Skin ageing is characterised by the emergence of wrinkles and spots, a loss of firmness and elasticity, as well as skin dryness. Discover the biological mechanisms behind these signs.
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How does our skin age?
Summary
- Focus on the structure of the skin
- The signs of skin ageing
- The biological processes behind these signs
- Source
Published February 23, 2024,
by
Sandrine, Scientific Editor
—
6 min read
Topics:
Focus on the structure of the skin.
The skin is composed of three layers, from the most superficial to the deepest:
Epidermis:
This is the most superficial layer of the skin. It contains several cellular populations (keratinocytes, melanocytes, Langerhans cells, etc...).
The keratinocytes are present at various levels of the epidermis. They synthesise keratin, a fibrous and water-insoluble protein, which gives the skin its waterproof nature. It thus protects the skin from external aggressions.
The primary role of the epidermis is its function of skin protection thanks to keratinocytes and the stratum corneum. Indeed, the stratum corneum is composed of various epidermal lipids that protect the skin from external aggressions and transepidermal dehydration. Moreover, it is covered with a hydrolipidic film that acts as an additional protective barrier. This hydrolipidic film is primarily composed of sebum secreted by the sebaceous glands.
The skin also contains melanocytes. Upon exposure to UV rays, melanocytes synthesise melanin, a pigment that serves to protect our skin from UV rays. Therefore, tanning is actually a defence mechanism of the skin!
Dermis :
It is at the level of the dermis that new skin cells multiply in order to replace those that are eliminated. Furthermore, the dermis contains the fibroblasts which synthesise collagen fibres, elastin, as well as hyaluronic acid, responsible for the density, elasticity and firmness of the skin.
Hypodermis:
Its primary role is to manage the storage and release of lipids. It also plays a part in thermoregulation.
The signs of skin ageing.
Skin ageing results from the combination of internal and external causes. It begins from the twenties.
The signs of skin ageing are a loosening of the skin, enlarged pores, the appearance of wrinkles, as well as spots or an increase in dryness.
The skin on the face is particularly affected by ageing, as it is continuously exposed to UV rays and pollution. Additionally, the facial muscles are constantly engaged with facial expressions.
The biological processes behind these signs.
Skin ageing is biologically characterised by changes at the level of the epidermis, the dermo-epidermal junction, as well as by the degradation of the dermal extracellular matrix:
The wrinkles :
Surface wrinkles are the most common. They are found in areas where facial expressions are significant, such as the areas near the eyes or mouth. Wrinkles are caused by skin dehydration due to an imbalance in its barrier function and by its thinning due to a decrease in keratin synthesis. Indeed, the more dehydrated and thin the skin is, the more pronounced the wrinkles will be.
Permanent wrinkles are the result of a decrease in collagen in the dermis and a modification of the extracellular matrix. Deep wrinkles are not initially visible unless’one smiles or frowns.’Over time, they gradually set in and alter the expression of the face. They are the result of repeated muscle contractions.
Decline in the skin's barrier function:
The composition of the skin's stratum corneum changes over time. A decrease in sebum secretion is observed, leading to a weakening of the hydrolipidic film. Consequently, the skin becomes more susceptible to damage and dehydration. This change also triggers a disruption in the skin's microbiota (dysbiosis). Furthermore, with age, there is a reduction in keratinocytes, which play a crucial role in skin protection.
Dull complexion and enlarged pores :
The cellular renewal of the skin gradually decreases, which promotes the accumulation of dead cells, leading to a dull complexion and enlarged pores.
Due to the repetitive contractions of the muscles in our face, the structure of the fibroblasts changes and they can no longer synthesise collagen and elastin fibres, as well as hyaluronic acid. We then observe a slowdown in fibroblast activity, resulting in a loss of elasticity, density, and firmness of the skin.
The number of melanocytes decreases by 6 to 8% every 10 years. As we age, our skin is therefore less protected from the sun. The appearance of pigmented spots is more significant in photo-exposed areas. This can be explained by a reduction in the natural elimination of cells filled with melanin due to the slowing down of skin renewal.
Source
DESMOULIERE A. & al. Skin changes during ageing. Subcellular Biochemistry (2019).
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