The safety of routine X-rays has been called into question following the unexpected discovery that cells exposed to low doses avoid or delay repairing damaged DNA.

Puzzlingly, cells given higher doses of X-rays were faster and more efficient at patching up any damage. But the German researchers who made the discovery say it is not clear whether the sloppy repairs that follow low level exposure is a good or bad thing.

Kai Rothkamm and Markus Löbrich, at the University of Saarland in Homburg, acknowledge that unrepaired breaks in DNA could well lead to cells becoming cancerous. But it is equally possible, they say, that the failure to repair low-level DNA damage has evolved as a safety measure.

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