Ageing is a complex biological process and affects several constituents of the skin and hence its appearance. There are two primary skin-ageing mechanisms, intrinsic and extrinsic. Genetic variations are thought to be the main cause of intrinsic ageing, determining the rate at which the skin ages. Extrinsic ageing instead is caused by environmental factors and in particular by sun exposure, also known as photo-ageing. Both intrinsic and extrinsic ageing act simultaneously and are associated with phenotypic changes in the skin such as wrinkles and sagginess. However, deep inside in the dermal layer of skin, collagen, elastin and hyaluronic acid, undergo different structural and functional changes. Collagen and elastin are large proteins and hence are pre-disposed to intrinsic molecular aging. These fibres accumulate damage over time and this decreases their ability to function correctly. Aged skin is generally characterised by reduced density of altered collagen fibres, elastin and hyaluronic acid.
Evidence indicates that the activation of matrix metalloproteinases play a major role in the pathogenesis of photoaging. Metalloproteinases can be induced by UVA and UVB and show proteolytic activity that results in the degradation of collagen and elastin fibres. As a result, the collagen density decreases each year at a faster rate in photo-exposed skin.