UVC uses specific wavelengths of electromagnetic radiation to kill bacteria and viruses. UVC waves are essentially a type of light wave, but they are invisible to the human eye and much more powerful than the light that comes out of a regular light bulb.
UVC works to kill bacteria and viruses by mutating their genetic material, making them unable to survive and reproduce. And when properly implemented, these systems are very effective. UVC disinfection can kill up to 99% of pathogens when used correctly and in the right environment.
But an interesting phenomenon has been long-observed when using UVC systems – a strange smell. For many years, scientists didn’t have an adequate explanation for the smell from UVC systems, which can be described as a pungent, rotten smell.
While the smell remained a mystery for many years, or was casually explained away by the production of ozone, over the last few years scientists have finally come to a stronger conclusion about just what makes UVC lamps so pungent.
Possible Hypotheses about UVC Odor
The study that really cracked the code as far as the UVC odor was published in 2018 by Normand Brais. In it, he points out a few of the things people have thought might cause the smell from UVC lamps that have been disproven. These include:
- Off-gassing from wall materials like paint: This would mean the smell is coming from the walls releasing toxins in response to UV light exposure. This type of thing can occur, but Brais’ study ultimately disproves it. Even when UV lamps were used in a room made of aluminum, with no paint at all, the smell occurred.
- Off-gassing glue or rubber components from UVC lamps: This is essentially the same thing, but with toxins coming from lamp components rather than from the walls. And the hypothesis was disproven in a similar way – when glue and rubber were removed from UVC lamps, they still exhibited the odor. This demonstrates that the odor is not caused by some random, easy-to-explain off-gassing.
The Conclusion: Dust Is to Blame
The same high energy that makes UVC lamps so good for disinfection also makes them destructive to other living tissues and organic matter. UVC is blocked by the atmosphere, so we are only ever exposed to UVA and UVB outside. This exposure gives us a slow, steady sunburn. But UVC is much more powerful and causes more damage more quickly. Sunburn can form in mere minutes in response to UVC exposure.
So when we deploy a UVC system to sterilize the air, those high-energy light waves are also hitting millions of particles of dust. Studies show that dust is mostly composed of dead skin cells and hair – up to 80% by volume. So these little bits of organic matter are fried by the high-energy UVC waves from your sanitation system.
Why Does UVC Damaged Dust Smell?
Hair and skin contain a lot of the amino acid cysteine and the larger molecule keratin, which is composed of long chains of cysteine. These compounds contain sulfur, to which our noses are especially sensitive.
When high-energy UVC hits these compounds, the bonds in them break. This can lead to the formation of smaller, sulfur-containing molecules called thiols and mercaptans. These are the types of compounds you can smell in rotting eggs or smelly vegetables like broccoli.
The smell-thresholds are so low for sulfur-containing compounds that even if the odor is strong, the room is extremely unlikely to contain an unsafe level of these compounds. It’s a bad smell – but a harmless one.
So if your UVC sanitizing lamp causes an odor – do not be alarmed. You can take that smell as a sign that your UVC system is working as intended.