It has been rumoured for as long as there have been cell phones and now there’s some research to back it up.

According to a recent report from Quartz Media, two federal studies have found “clear evidence” that mobile phone radiation is the direct cause of heart cancer in male rats. The results of the studies will have a significant effect on the debate regarding whether mobile phone radiation causes cancer or not.

Until now, it was believed that mobile phones were not the cause of cancer as they emit non-ionizing radiation, and the federal government and manufacturers worked under this presumption. However, the studies conducted by the US National Toxicology Program have found that exposure to radiation cased heart tumors in male rats and found “some evidence” that it also cause tumors in their brains.

Tumors were also found in the hearts of female rats, but the data didn’t rise to the level of statistical significance and the results were therefore labeled “equivocal”, meaning that the researchers couldn’t be sure if the radiation caused the tumors or whether they occurred naturally. The next step in the process is to determine the effects of the radiation on humans. The papers will now be passed on to the US Food and Drug Administration, which is responsible for determining human risk and issuing control guidelines to prevent the same.