Hacker News Reader

Comment by mrfusion | Hacker News Reader

Don’t forget that we actually need exposure to germs to train our immune systems. We don’t want to overdo sanitizing everything.

Look up the hygiene hypothesis.

View on HN

Right - I also don’t like the idea of something indiscriminately killing bacteria on my skin and food. Microbiomes in and around our body shouldn’t be messed with unnecessarily IMO.

OTOH this is a type of ultraviolet exposure that we would also receive from sunlight. At least as claimed, it's not doing anything different to our microbiomes than just going outside would do.

No, it's not. You might see UV-A or UV-B in normal sunlight, but not UV-C. It is blocked by the atmosphere. That's why it's so dangerous to terrestrial life as diverse as viruses, bacteria, and human beings, as well as others.

UV-C is not something we have had frequent exposure to over the millennia, and so this is something we are not adapted to handle.

Ugh, you're absolutely correct! I retract my prior comment; thanks for the correction. And not to detract from my being flat-out wrong, but it should be noted that it's claimed that the specific 222nm wavelength of far-UVC used by these devices is not energetic enough to penetrate the skin or lens of the eyes [0][1].

[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5552051/

[1] https://journals.plos.org/plosone/article?id=10.1371/journal...

That's not how it works, unfortunately. Lower wavelength light has more energy and is in general more penetrating and more dangerous. But the particular behavior of any given material (due basically to resonances) can and will dominate the overall response.

Your references are rather disingenuous in that they only look at the skin, not the eyes (at least, I think that's what the abstracts are saying; I've never spoken "pretentious Latinate doctor" very well at all) and look for "typical" UV damage biomarkers... which is pretty stupid when you're not using "typical" UV light.

So, maybe safe, but the analysis so far doesn't really pass the smell test. Establishing safety of something like this, for the intensities needed, isn't an easy task.

I have no involvement in this industry, neither academically or by investment. Just on a learning journey, like many here. Disingenuous? It does me no good to deny that accusation, but I think the discourse level here is higher if we dispute each other's facts over disputing each other's motives. You appear to have a much more deeply rooted interest than I on this subject, and I have no reason to dispute your facts, but as for your opinion that "it doesn't pass the [ocular] smell test," a web search turns up, "the reason is that far-UVC light has a range in biological materials of less than a few micrometers, and thus it cannot reach living human cells in the skin or eyes, being absorbed in the skin stratum corneum or the ocular tear layer."[0]

You're undoubtedly already familiar with that so I'm sure there's some reason you have for finding it less than conclusive. In any event, I totally agree with you that the safety of this needs to be firmly established before releasing 222nm lamps for general home use, although I think a more limited use might be acceptable (for example, placing the bulb in a UV-opaque enclosure and circulating the room air through that unit).

[0] https://www.nature.com/articles/s41598-020-67211-2

To be clear, I was calling the researchers who wrote those papers disingenuous, not you. I've reviewed scientific papers. I have seen some true garbage. This is probably why I have a pretty low tolerance for bad papers or paper puffery. Those papers are skirting around inconvenient facts to make their conclusions appear stronger, which they should not be doing. Nothing is wrong per se, it's just intentionally not clear.

As an example of what I mean, take the Buonanno paper you linked. They say "We measured induction of the two most abundant premutagenic DNA lesions in the epidermis, cyclobutane pyrimidine dimers (CPD) and pyrimidine-pyrimidone 6-4 photoproducts (6-4PP) (4), as a function of UVC fluence in 3D human skin constructs immediately after exposure using the immunohistochemical approach previously described (7)."

It's natural to ask the question, is that the right thing to measure? There is no reason to suspect that 222nm and 254nm light will cleave the same bonds, so you might get a completely different set of dissociation products. Reference [7] has nothing to say on this subject (plus is citation incest) and in fact links back (as Reference [16]) to Reference [4], so that's the one. Except... it doesn't support this claim. At all. In fact it kind of suggests the opposite, that you can get pretty wide variation here depending on the incoming light: "In addition, we showed that the sequence distribution of CPDs induced by natural sunlight is very different from that induced by UVC (254 nm) at sequence positions specifically containing 5-methylcytosine bases."

So when I find crap like that in a paper that has a general air of puffery (as one, regrettably, must often take on these days in order to secure funding), I get really damn suspicious. I am not claiming anything is wrong, or that any claims are false. I am simply saying that the provided evidence is not sufficient to establish at least one of the paper's claims, and the authors are not forthright about it.

You could build a shade for the light or put it in some ventilation system or air purifier so that only airborne particles get killed.

That's a standard thing you can add to air handlers. We have UV-C bulbs in our own air handler units upstairs in the attic. They're expensive, though.

Reply on news.ycombinator.com