The mechanisms of skin ageing - what happens and why

Intrinsic ageing: the biological clock

Intrinsic ageing is genetically programmed and occurs independently of environment. From approximately the mid-twenties, collagen production decreases by roughly 1% per year. Elastin fibres become less resilient. Epidermal cell turnover slows, from approximately 28 days in young skin to 40 to 60 days in older skin, meaning damaged cells are replaced more slowly and the skin surface is less consistently renewed.

The dermis gradually thins. Subcutaneous fat redistributes. Bone resorption in the facial skeleton alters the structural support beneath the skin. These changes are intrinsic, predictable and cumulative. And they form the baseline over which all extrinsic factors operate.

Extrinsic ageing: the environmental drivers

Extrinsic ageing is driven by environmental and lifestyle factors. UV radiation is the dominant contributor, accounting for an estimated 80 to 90% of visible facial ageing (Flament et al., Dermatoendocrinology, 2013). Other significant contributors include chronic low-grade inflammation (inflammaging), oxidative stress, glycation, smoking, and the mechanical stress of repeated facial muscle contractions.

The practical implication: Because extrinsic factors dominate visible ageing, most of what we observe is substantially modifiable. Daily SPF, anti-inflammatory lifestyle factors, and targeted clinical treatments address the pathways responsible for the majority of visible change.

Collagen and elastin show a structural decline

The dermis is composed primarily of collagen (approximately 70 to 80% of dry weight) and elastin. Collagen provides tensile strength and resistance to structural deformation. Elastin provides recoil, which is the ability of skin to spring back after movement. Both decline with age and UV exposure.

Collagen degradation is driven by matrix metalloproteinases (MMPs), enzymes whose activity is significantly upregulated by UV exposure and inflammatory signalling. As the collagen matrix degrades and new collagen synthesis declines simultaneously, the dermis thins and loses structural integrity. Most clinical treatments for skin ageing address this pathway directly: Botox reduces mechanical stress, polynucleotides and PRP stimulate fibroblast activity, microneedling triggers collagen induction, and IV infusions provide the building blocks collagen production requires.

Glycation: sugar-related collagen damage

Glycation is the non-enzymatic reaction between glucose and proteins including collagen and elastin. The resulting advanced glycation end-products (AGEs) cross-link protein fibres, stiffening them and making them less functional. Glycated collagen is stiffer, more brittle, and less able to provide the flexible structural support that keeps skin looking firm.

Glycation accumulates over time and is accelerated by chronically elevated blood sugar. It is a significant but underappreciated driver of skin ageing and one of the mechanisms targeted by L-Carnosine in the Skin Rejuvenation Infusion formulation.

Oxidative stress and reactive oxygen species

Oxidative stress occurs when reactive oxygen species (ROS) exceed the skin’s antioxidant capacity. ROS are unstable molecules generated by cellular metabolism, UV exposure, and environmental pollutants. ROS damage cellular structures including DNA, lipids in cell membranes, and structural proteins including collagen fibres.

The skin’s antioxidant defence system (including glutathione, Vitamin C, Vitamin E, and enzymatic antioxidants) neutralises ROS under normal conditions. With age, UV exposure, and lifestyle factors, this system becomes less efficient. Supporting antioxidant capacity through topical SPF, dietary polyphenols, and targeted supplementation directly addresses this mechanism.