For years, people have blamed phones and the radiation they emit as potential causes of cancer.
Though that theory still remains unproven, America's National Toxicology Program has been able to associate radio frequency radiation emitted by 2G, 3G cell phones with cancerous tumors in rats.
They conducted experiments for more than 10 years and found some clear links.
Here are the findings.
What the experiments found?
According to NTP's results, high levels of radio frequency radiation (RFR) similar to that used in 2G, 3G phones leads to cancerous heart tumors in male rats.
They also found some evidence of tumors in the brain and adrenal glands of male rats due to similar exposure.
However, the cases of female rats, as well as male and female mice, still remain unconfirmed.
How the experiments were conducted?
For the study, rats and mice were placed in specially designed chambers and exposed to high levels of RFR for up to two years - nine hours each day.
They were exposed to much higher RFR than exposure allowed for typical cell phone users.
Specifically, the minimum radiation exposure in the experiment was the maximum level permitted for humans, which rarely occurs.
This isn't a direct model for humans, but could help
While these experiments could prove critical in understanding the impact of RFR on humans, it is imperative to note these results cannot be applied to the case of humans, at least not directly.
This is mainly because the levels of radiation used were much higher and the entire bodies of the animals were exposed.
In humans, exposure only occurs where the phones are kept.
Also, the study didn't investigate 4G, 5G, or Wi-Fi RFRs
Notably, the researchers didn't investigate the impact of RFRs from 4G, Wi-Fi, or 5G devices. "5G is an emerging technology that hasn't really been defined yet," said study lead Michael Wyde. "From what we currently understand, it likely differs dramatically from what we studied".