How can light kill pathogens?

4 minute read

When someone encounters ultraviolet (UV) sanitization technology for the first time, their initial reaction is usually something like, “Wait…what? Light? Really?”

Yes, really.

“Simply put: UV light damages a cell’s DNA. With enough damage, the cell dies.”

To have a full appreciation of how it works, however, we’ll have to go down to the pathogen scale—about 10–20 times the size of a single atom. Really, really small. Once you’ve adjusted to your new microscopic surroundings, we need to discuss the two main components of the question at hand: UV light and cellular DNA.

First, UV light. On the human scale, light rays are the source of a warm glow and the occasional sunburn. On the microscopic scale, however, they’re lethal projectiles. These photons are infinitely small beams of energy, whizzing through space at 670,000,000 mph (yes, you read that right: 670 million miles per hour). They’ll rip through just about anything.

The “ultraviolet” part of the light comes from the particular wavelength of the particle. UV light has a shorter wavelength than the violet range of the visible spectrum (hence its name). And in the world of wave particles, shorter wavelengths mean greater energy. Depending on the frequency, ultraviolet light can pack thousands of times more energy than visible-spectrum light. If light particles are bullets, UV light particles were fired from a sniper rifle.

Next, DNA. You may recall from science class that DNA forms a double helix shape; pairs of acid bases joining to form “rungs” in the twisting ladder. When UV light hits DNA, the rungs break apart and reconfigure in unexpected ways (into what scientists call a “dimer”). If DNA is a cell’s hard drive, dimers are the file corruptions.

One DNA error alone isn’t usually a fatal blow. Most cells (both human and non-human) have error-correction capabilities that help solve for the unexpected data corruption. With enough damage, however, even the most elegant correction systems can’t keep up—the cell can no longer replicate itself, and it’s rendered functionally inert.

Alright, that’s enough microscopic murder for one post. Let’s leave the nanometer scale and return back to full size, where the simple act of turning on a lightbulb won’t cause a panicked emotional breakdown. But next time you’re out in the sun, spare a thought for your cells’ existential war. And maybe put on some sunscreen.

Related Questions

Wait, shouldn’t I worry about exposing myself to UV light?
Maybe, but not excessively. While UV light does pose the same risk to human cells that it does to pathogen cells, humans have the advantage of redundancy. If you’re a trillion-celled human, damaging one cell’s DNA isn’t that big of a deal. If you’re a single-celled bacterium, however, it’s pretty much game over. Of course, that doesn’t mean you should be cavalier about UV light safety—avoid uncovered UV light sanitizers, use sunscreen as directed, etc. But for most people, normal interaction with UV light shouldn’t be keeping you up at night.

Aren’t home UV sanitizers dangerous, then?
For pathogens? Absolutely. For humans? Not at all. So long as the UV light doesn’t leak out into the surrounding area, light-based sanitization systems are perfectly safe. Yes, there’s a controlled reaction happening inside that would pose risks if not properly harnessed—but the same is true for your car engine (combustion), your computer (electricity) and just about every other technology you use. It’s pretty simple: UV light is only unsafe if it’s not used safely.

In fact, the best UV-C sanitizers like Airetrex 365 have reflective chambers that allow the UV light to bounce around inside and collide with more pathogens without posing any risk to the people in the area.

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