Epigenetics and ultraviolet radiation: Implications for skin ageing and carcinogenesis.

Recent published data have highlighted the importance of epigenetics in the response of the skin to recreational and therapeutic ultraviolet radiation (UVR) exposure. 'Epi'-from the Greek επί, meaning over, outside of or around-relates to the chemical modifications that occur on top of the DNA sequence (for example, DNA methylation) and its associated proteins (e.g. histone modifications, including methylation, acetylation and phosphorylation). These epigenetic processes, collectively called the 'epigenome', dictate the three-dimensional conformation of the DNA, thus impacting upon gene expression and genomic stability. Given that epigenetic changes are long-lived and mitotically heritable, an accumulation of epigenetic perturbations likely influence the pathogenesis of the chronic consequences of UVR exposure, including photoageing and skin cancer risk. In this review, we describe the multifarious epigenetic effects elicited by UVR in the skin. We further speculate on the underlying molecular mechanisms that may direct epigenetic changes, such as oxidative stress and changes in metabolism, and their impact on skin health and disease.