DNA damage in general and DNA strand breaks in particular occur every day in all cells of the human body. This is due to internal influences such as free radicals, which are produced during inflammatory processes and cellular respiration, and external ones, such as cosmic background radiation or X-rays in the course of medical diagnostic measures. DNA strand breaks can lead to cell death or to mutations and thus contribute in the long term to cancer development or the aging process.
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Source: Phys.org