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Why can large doses of X-rays increase the risk of cancer?

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Diagram of the electromagnetic spectrum showing different types of waves arranged by wavelength and frequency, from gamma rays and X-rays to ultraviolet, visible light, infrared, microwave, TV/FM radio, shortwave radio, AM radio, and longwave radio. — X-ray The relationship of X-rays to other electromagnetic radiation within the electromagnetic spectrum.

Large doses of X-rays increase the risk of cancer because they are a form of ionizing radiation that can cause significant biochemical and genetic damage to living cells.21

When high-energy X-ray photons pass through tissue, they liberate electrons from atoms and molecules, creating reactive ions and free radicals. These particles can break molecular bonds, including the double-stranded DNA within a cell's nucleus. While cells possess DNA repair mechanisms to fix such damage, these processes are not always perfect.2345

If DNA lesions remain unrepaired or are misrepaired, they can lead to permanent genetic mutations or chromosomal damage. When these mutations affect genes responsible for regulating cell growth and division, they can trigger neoplastic transformation—a process where cells begin to grow and divide uncontrollably, potentially leading to the development of cancer. Because this damage is cumulative, the risk of developing radiation-induced cancer generally increases with the total dose of radiation absorbed by the body.4617