Photoageing: the darker side of the sun

Abstract

Photoageing is a consequence of chronic exposure to solar ultraviolet irradiation. Wrinkling appears to be the result of reduced extracellular matrix synthesis within the dermis accompanied by enhanced matrix remodelling by specific endopeptidases (matrix metalloproteinases) and proteases. Furthermore, it appears that the local hormonal milieu can influence the mechanisms that culminate in photoageing. In this review, we discuss the changes that occur in the extracellular matrix of photoaged skin and the mechanisms by which they are modulated. Cutaneous ageing can result from either the passage of time (intrinsic ageing) or from environmental influences, such as chronic sun exposure (photoageing). Intrinsic (chronological) ageingof the skin is a subtle process similar to the ageingof internal organs, causing slow deterioration of skin. Histological changes are not evident until old age (≥70 years), the skin becoming gradually dry, pale and finely wrinkled, exhibiting an overall dermal atrophy and reduced amounts of fibrillar collagens and elastic fibres. Photodamage is the most important environmental factor superimposed upon intrinsic ageing and is exemplified by rough dry skin with mottled hyperpigmentation and marked loss of elasticity and recoil. The combination of photodamage and intrinsic ageing is termed photoageing (Fig. 1). Recent experimental data indicate that involvement of the endocrine system and other environmental influences (for example, smoking) can act as accelerating factors to the photoageing process.