DNA methylation is a chemical modification in which methyl groups are added to DNA, typically at cytosine bases in CpG sites. It does not change the DNA sequence but strongly affects how genes are used. In general, high methylation in gene promoters is associated with gene silencing, while low methylation can allow gene activation.

During early development, the methylation pattern of the genome is extensively reprogrammed. Large waves of demethylation and remethylation help establish cell identity. As cells specialize, they acquire stable, cell type specific methylation signatures that control which genes stay active. Errors in these patterns contribute to developmental disorders.

In adulthood, methylation patterns continue to change with aging and environmental exposure. Characteristic age related shifts in methylation at specific genomic sites are so consistent that they can be used as “epigenetic clocks” to estimate biological age. Lifestyle, diet, stress, and toxic exposures can accelerate or slow these epigenetic changes.

Aberrant DNA methylation is a hallmark of many diseases, especially cancer. Tumors often show global hypomethylation that destabilizes the genome, along with hypermethylation of particular tumor suppressor genes that helps malignant cells grow. Measuring methylation in blood or tissue is being developed as a tool for early cancer detection and prognosis.

Research is also exploring whether interventions such as drugs, dietary factors, or changes in environmental exposures can modify methylation patterns in ways that improve health. Overall, DNA methylation research connects gene regulation, development, aging, environment, and disease in a single biochemical framework.