I mean, UV light is carcinogenic, and environments that are way too clean, are fine for surgery or manufacturing semiconductors, but for most humans (specially children) they can be counter-productive.
The immune system needs something to train on and fight, otherwise you end up with autoimmune diseases and all sorts of crap.
We're essentially walking ecosystems that can easily be imbalanced.
Far UVC is carcinogenic when it reaches living tissue. However, it has a very short mean free path so it doesn't, generally, reach the growing layer of skin. It's less obvious whether exposed mucus membranes (lips, nose, tongue) or the eyes are affected. It probably doesn't reach the lens of the eye, which is good.
The tear layer only contributes a little bit--far-UV eye safety is mostly down to the fact that the 222nm only penetrates to outer epithelium (so cells that will be dead in a few days anyway), and the fact that your eyes get very little effective dose if you aren't staring directly into the lamp. You've got eyelids, eyelashes, eyebrows, hair, etc, so the effective dose to your eyes is actually much lower than the dose assumed by most safety standards (ANSI/IES 27.1-22, UL8802), which are fairly conservative. Check out this paper http://onlinelibrary.wiley.com/doi/abs/10.1111/php.13671
That is not true. It can cause possibly eye irritation but animal trials have shown that it is not carcinogenic even to mucus membranes, eyes, and thin-skinned areas.
The best training for immune robustness is going outside and get exposure to a wide range of stuff. But for indoor spaces, air quality is going to be dominated by the microbes and viruses of the people in the space itself. For public spaces and shared residential spaces with poor airflow this would be great - grocery stores, nursing homes, etc. For condos, apartments, SFH, etc. it's probably less necessary, but probably wouldn't hurt. Or nice to have when company comes over, or someone in the house is sick and "polluting" the air.
I mean, UV light is carcinogenic, and environments that are way too clean, are fine for surgery or manufacturing semiconductors, but for most humans (specially children) they can be counter-productive.
The immune system needs something to train on and fight, otherwise you end up with autoimmune diseases and all sorts of crap.
We're essentially walking ecosystems that can easily be imbalanced.