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What are the causes of skin aging?

Intrinsic aging of the skin is a normal physiological process. However, it can be accelerated by extrinsic factors. Here's an overview of the causes of skin aging.

Summary
Published February 23, 2024, by Sandrine, Scientific Editor — 5 min read

Intrinsic aging of the skin.

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

  • Oxidative Stress:

    In aerobic living organisms, oxygen generates compounds known as reactive oxygen species (ROS) under normal physiological conditions (respiratory chain, peroxisomes, etc.). However, under certain conditions, ROS can damage the body's tissues. To protect themselves, living organisms have developed an antioxidant defense system. When this defense system is overwhelmed, the ROS exert harmful effects on the body, a phenomenon known 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 aging.

  • 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 aging is also explained by hormonal variations. Indeed, hormones decrease with age, and this is at the root of skin aging. For example, the estrogens that stimulate collagen synthesis and increase hyaluronic acid synthesis, drop at menopause. This causes skin dehydration, promoting the appearance of wrinkles, thinning of the epidermis, and impaired wound healing. DHEA, which acts against aging, 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 aging, due to the fibroblast senescence.

Extrinsic aging of the skin.

As previously mentioned, the skin undergoes an intrinsic aging process, also referred to as chronological aging. This process 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 aging, characterized by the early onset of wrinkles, pigmentation spots and a sagging and dried out skin. This aging is due to an abnormal accumulation of elastic fibers (solar elastosis) and a decrease in collagen fibers in the dermis, due to the genotoxic effects of UVB rays. Indeed, their impact on DNA triggers the expression of molecules that disrupt the network of collagen fibers. In the long term, due to their genotoxicity, UVA and UVB rays cause the appearance of cancerous cells (melanomas).

  • Tobacco:

    Smokers generally experience 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, typically found in the periorbital areas and in the "crow's feet" region. There are multiple mechanisms explaining the effects of tobacco on skin aging.

    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 corneal layer. Moreover, a dehydrated skin develops signs of aging more rapidly.

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

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

  • Pollution:

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

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

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

Sources

  • 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).

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