Ageing is a complex process that results in the decline of the body’s biological functions, leading to a less efficient way of coping with the metabolic stresses of time. Although many cultures refer to older people as a source of wisdom, in Western society people are refusing to age1. As the skin reflects the general inner health and perceptions of beauty in a person, more people are seeking interventions to retain a youthful appearance. The global skincare market is predicted to increase in revenue from $79.3 billion in 2012, to a value of $102.3 billion by the end of 20182.
The mechanisms of cutaneous ageing are traditionally divided into intrinsic or chronological ageing, and extrinsic ageing, which is influenced by environmental factors3. In this article, the mechanisms and pathways of skin ageing are outlined, with a focus on the interventions that have been proven, or have potential, to improve the appearance of ageing skin. The relevant information was compiled using a MEDLINE search from January 1966 to July 2013 with the following keywords: ‘skin ageing’, ‘dermal ageing’, ‘skin physiology phenomena’, ‘oestrogen replacement therapy’. ‘nutrition and skin ageing’, ‘photoageing’, and ‘anti-skin ageing interventions’.
Skin anatomy and physiology
The skin is the largest organ in the body and serves as a primary barrier against foreign material, while also protecting the internal organs from the external environment. Other functions include: protection against radiation, thermal regulation, sensory detection, biochemical synthesis, and regulation of water and electrolytes. It is a complex organ with multiple structures and a mosaic of cells. It is divided into the epidermis, dermis and hypodermis (Figure 1). Hair follicles, sebaceous glands and sweat glands are also present in the human skin4.
The thin epidermal layer is made up of keratinocytes, melanocytes and antigen-presenting Langerhans cells. Between the epidermis and dermis, there is a basement membrane which mainly contains extracellular proteins produced by fibroblasts4. The dermis forms the main bulk of the skin and is the deepest layer, with the vascular and nerve supply of the skin residing in this layer. The dermal connective tissue is made up of collagen and elastin, with collagen forming 80% of the dry weight of the skin4. Type I collagen is the most abundant collagen in the connective tissue, with types III, V and VII found in lesser amounts5, 6. Procollagen fibres are synthesised by fibroblasts and after undergoing enzymatic processing, they form a triple helix configuration and arrange parallel to the skin’s surface. This enhances tensile strength and prevents the skin from overstretching7. Elastin is also produced by fibroblasts, but it only forms 5% of the dermis and is a thinly distributed subepidermal network. Other than collagen and elastin, extracellular proteins also include proteoglycans and fibronectin. The third layer of the skin is the subcutaneous tissue, which comprises fat cells that underline the connective tissue network of the dermal layer4.
Pathomechanisms of intrinsic skin ageing
Intrinsic (chronological) ageing is a natural consequence of ageing. It is a genetically predetermined process in which the skin, with the passage of time, becomes thinner, atrophic, finely wrinkled and dry. The support of this theory comes from the fact that the terminal portions of telomere chromosomes shorten by approximately 100 base pairs with every cell cycle8.
Clinically, older skin looks atrophic as it contains thickened, clumped collagenous proteins, indicating partial degeneration of collagen. Histological findings show a general decrease in the extracellular matrix (ECM), with reduced collagen and elastin9. This is partly owing to a reduction of fibroblasts, as well as a reduction in hydroxyproline and glycosylated hydroxylysine enzymes, which are responsible for post-transational processing of type I collagen10. All of this eventually leads to decrease in skin laxity and formation of wrinkles.