Step 1 so far has been Wikipedia, where I found the reassuring sentence "The scientific consensus is that 5G technology is safe.[99][100][101]" Unfortunately, after checking those sources it appears that one is a blog and the other two are news articles about the same event - a press release from the ICNIRP. Further research on the ICNIRP shows that it is a private organization that declared itself that it only considered the thermal dangers of RF in the cm-wave range, and any other dangers do not exist.
And that is the common path to "proving" 5G safety on the internet: "the only way that this could be bad is heating; there's no heating; bam, it's safe, we're done here."
The reality, of course, is that EM waves have many mechanisms of action. So far, we know of the following:
- Ionizing radiation (nuclear weapons, x-rays, etc) can easily kill you or give you cancer
- Non-UV visible light can increase skin aging, cause retinal injuries
- Tons of EM waves can burn you or increase body temperature causing other problems (tissue heating)
- Nerve disturbance from low-frequency RF
That's four methods of ways EM waves can hurt you. Everyone is in agreement about that - no matter how you slice it, there's a minimum of those four. But that's a minimum. Relatively few good quality longitudinal studies have been run about EM waves. "Hey, can we put this weird thing in your home and see if it gives you cancer?" is a hard sell, I guess.
But unfortunately there seems to be not one single high-quality, longitudinal study researching the effects of living with constant mm-wave sources. There are a few short-term studies, but most of these are on the order of hours (!) of exposure.
One interesting thing I did find was a Swiss study showing people living near high voltage power lines were more than two times more likely to get Alzheimer's than people living just 600m away. While that's a completely different type of EM than 5G, it does hint that there may be more harmful mechanisms of EM radiation than we currently know.