DNA is an inert molecule, exquisitely resistant to most chemical reactions, for its job is to maintain the stability of genetic information. But X-rays can shatter strands of DNA or generate toxic chemicals that corrode DNA. Cells respond to this damage by dying or, more often, by ceasing to divide. X-rays thus preferentially kill the most rapidly proliferating cells in the body, cells in the skin, nails, gums, and blood.
