What are the causes of skin ageing?

Like all other organs in our body, the skin is subject to an intrinsic ageing process that is caused by 3 factors:

• Oxidative Stress:

  In aerobic living organisms, oxygen generates compounds known as reactive oxygen derivatives (ROD), under normal physiological conditions (respiratory chain, peroxisomes, etc...). However, under certain circumstances, these ROD can damage the body's tissues. To protect themselves, living organisms have developed an antioxidant defence system. When this defence system is overwhelmed, the ROD exert harmful effects on the body: this is referred to as oxidative stress. This stress leads to DNA breaks and mutations, oxidation of sugars (glycation), lipid peroxidation, as well as inactivation of proteins and enzymes which are at the root of cellular ageing.

• Telomere Shortening:

  Telomeres are repetitive DNA sequences at the end of chromosomes. Their role is to preserve the integrity of the genetic heritage. Each time a cell copies its DNA before dividing, it loses a piece of telomere. The more the telomeres shorten, the more the cell ages.

• Hormonal Variations:

  Intrinsic skin ageing is also explained by hormonal variations. Indeed, hormones decrease with age and this is at the root of skin ageing. For example, the oestrogens that stimulate collagen synthesis and increase hyaluronic acid synthesis, drop at menopause. This causes skin dehydration, promoting the appearance of wrinkles, a thinning of the epidermis, as well as a healing defect. DHEA, which acts against ageing, and melatonin, which combats free radicals, also decrease with age.

In parallel to this hormone reduction, the TGF-beta-1 increases, which is also responsible for skin ageing, due to the fibroblast senescence.

As previously mentioned, the skin undergoes an intrinsic ageing process, also referred to as chronological ageing. This can also be exacerbated by extrinsic factors such as:

• The UV rays :

  The harmful effects of the sun on the skin are well established. Indeed, in the medium term, UVA and UVB rays lead to premature skin ageing, characterised by the early onset of wrinkles, pigmentation spots and a sagging and dried out skin. This ageing is due to an abnormal accumulation of elastic fibres (solar elastosis) and a reduction in collagen fibres in the dermis, caused by the genotoxic effects of UVB rays. Indeed, their impact on DNA triggers the expression of molecules that disrupt the network of collagen fibres. In the long term, due to their genotoxicity, UVA and UVB rays cause the emergence of cancerous cells (melanomas).

• Tobacco:

  Smokers generally experience an earlier onset of wrinkles, as well as a duller complexion: this is what is referred to as "cigarette skin". The wrinkles of smokers are narrower and deeper, and are typically found in the periorbital areas and in the "crow's feet" region. There are multiple mechanisms explaining the effects of tobacco on skin ageing.

  Firstly, tobacco smoke increases insensible water loss, leading to the dehydration of the stratum corneum. This results in a reduction of the thickness of the horny layer. Moreover, a dehydrated skin develops signs of ageing more rapidly.

  Next, similar to UV rays, tobacco use results in an abnormal accumulation of elastic fibres, as well as a reduction in collagen fibres.

  Tobacco also reduces the secretion of oestrogens, as it increases the hydroxylation of oestrogens. These oestrogens play a role in skin biology by stimulating collagen synthesis and increasing the synthesis of hyaluronic acid. Furthermore, tobacco contains substances known to be responsible for oxidative stress and lipid peroxidation.

• Pollution:

  A study has proven that the higher the pollution level, the more individuals exposed develop age spots. Pollution particles can be absorbed at the skin level via intercellular pathways. Within the body, pollution particles are capable, through genetic mechanisms, of accelerating skin ageing by increasing inflammation, hyperpigmentation and reducing collagen production.

Note : Other external factors could potentially accelerate chronological ageing, such as malnutrition, alcohol or even stress.

However, it is important to know that UV rays contribute to 80% of premature skin ageing.

• PUIZINA-IVIC N. Skin aging. Acta Dermatovenerologica Alpina Pannonica et Adriatica (2008).

• HUMBERT P. & al. Tabac et peau. Annales de Dermatologie et de Vénérologie (2010).