Again, non-ionizing radiation — the radiation from cellphones — doesn’t have enough energy to break our DNA, and therefore, we have traditionally thought, it couldn’t cause cancer. But there is some question about whether it’s as harmless as was once believed, or whether there might be another mechanism at play, other than direct DNA damage, that could lead to cancer or other biological problems.
The energy of electromagnetic radiation is determined by its frequency; ionizing radiation is high frequency, and therefore high energy, whereas non-ionizing radiation is low frequency, and therefore low energy. The NCI fact sheet Electromagnetic Fields and Cancer lists sources of radiofrequency radiation. More information about ionizing radiation can be found on the Radiation page.