We’ve known for 100 years that there are microbes that don’t do well in ultraviolet light. UV radiation, whether from the sun or from lamps, seems to damage genetic material, which sabotages germs’ ability to replicate.
UV light works well enough on enough bugs that it’s a routine part of hospital disinfection.
UV light may turn out to kill COVID-19 viruses on surfaces, but we actually don’t know yet. It is a reasonable thing to expect, but no data have been released so far, so we can’t be sure.
There is one thing that is sure, though. If you have a COVID-19 infection, sitting in the sun or lying in a tanning bed will NOT cure you. Nor will the light kill all the viruses around you, and keep you safe from ever getting an infection. (Moving to a hot and humid climate won’t either.)
Infections don’t work like that. And if UV light (or the weather) could do what internet memes are claiming, we would have no viral infections on earth.
And no, making the UV light really bright won’t somehow make it work, as recent speculation has had it, and neither will inserting light bulbs into body cavities.
What ultraviolet light will do, if you give it long enough, is damage the genetic material in your skin cells, just as it does to viruses. We’ve written about this quite a lot. If you bake in the sun, you raise your chances, significantly, of developing skin cancer. If you hold your hands under a UV light to sterilize them, it may be that you'll kill bugs, but you’ll be doing something you could manage safely with soap instead.
Is there any connection at all, between getting some light on your skin and fighting infection?
Actually, there probably is, but it’s not because light kills microbes. One known mechanism behind light and immunity is vitamin D synthesis. We wrote about this a few weeks ago. There is also a nitric oxide pathway, that may explain even more of the undeniable association between (moderate) sun exposure and overall good health. This is still new, but the data are quite compelling. We’ll post a separate blog about this. It’s very interesting.
But as for killing viruses, it is simply not true that ultraviolet light, at any wavelength or any intensity, will destroy the bugs inside you, or safely sterilize the space around you, curing you of your COVID-19 infection or keeping you from ever getting one.
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