What is DNA?
Deoxyribonucleic acid
DNA is a very long molecule inside your cells that stores the instructions for building and running your body, written in a code of just four chemical "letters".
Think of DNA as a giant cookbook kept in every cell. Each recipe in it tells the cell how to make one specific thing it needs. The cell reads the recipes it needs, when it needs them, and copies the whole book every time it divides.
Why it matters for aging
Nearly every cell in your body carries a full copy of your DNA. Stretched out, the DNA in a single cell would be about two meters long, folded into a space far smaller than the tip of a pin. Most of it sits in the nucleus, the cell's control center. A small separate piece lives inside your mitochondria, the cell's power plants.
DNA is constantly under attack, from copying mistakes, sunlight, smoking and normal chemical wear. Your cells fix most of the damage, but repair isn't perfect. Damage that slips through and builds up over the years is one of the twelve hallmarks of aging, the main processes scientists agree drive aging. Scientists call it "genomic instability".
A common myth
Your DNA is fixed from birth, so your health is written in your genes.
The letters of your DNA barely change, but which recipes get read changes a lot with how you live: sleep, food, exercise and stress all switch genes on and off. DNA also picks up damage and typos over a lifetime, and your cells spend a lot of energy repairing it.
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Updated Nov 7, 2026 · All terms