Abstract: DNA methylation,which refers to a chemical modification process in which a methyl group is covalendy binding to the 5-position of the cytosine ring in CpG dinucleotides to form 5-methylcytosine under the catalysis by DNA methyltransferases (DNMTs),is a key epigenetic modification for gene regulation and mutation.Recent studies have shown that aberrant DNA methylation patterns exist in photoaged skin and ultraviolet radiation-induced skin tumors,which may be caused by decreased expression and activity of DNMT1,base excision repair and nucleotide excision repair,growth arrest,DNA-damage-inducible protein 45 alpha (Gadd45a)-mediated DNA demethylation,and so on.