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I've seen several manufacturers make the claim that UV-C air purifiers can prevent the common cold and flu - primarily due to the destruction of viruses. (The ones that only purify air by filtering do not make this claim.)

For example:

  • US Air Purifiers

    Though it requires more specialized equipment, there are several air purifiers that can kill off viruses and lower your risk of getting a cold during cold season. These units use UV light to kill off cold viruses, rather than capturing them with a filter. Since viruses are so small, this is by far the best way for an air purifier to attack the common cold virus. [...] These air purifiers can all kill off not just the common cold, but also most other viruses. Though this doesn’t guarantee you won’t get a cold this winter, it will significantly reduce your overall chances.

  • MicroLux, via a retailer:

    Using seven types of filtration to clean the air, the MicroLux will reduce the spread of colds and the flu by eliminating airborne bacteria, viruses, germs, and mold spores.

Is there any direct evidence to support this claim? Is it simply assumed to be true since UV-C is able to destroy viruses?

This related question is about purifiers based on HEPA filters, rather than ultraviolet filters: Do household air purifiers prevent illness?

  • 1
    If... Hard UV can destroy Virus' then it may help to prevent them entering the room or circulating in the air. But it won't stop the person with a streaming cold from touching the office door handle. So your real task is to find out what causes most cases of cold.. airborne.. or contact based infection. – Richard Nov 25 '18 at 23:11
  • Expanding upon Richard's comment--beware that "reduce" doesn't necessarily mean the reduction is noticeable. If it zapped every airborne virus particle (not possible as it doesn't instantly filter all air) but only 1% of transmission was that way it wouldn't do much but it would "reduce". – Loren Pechtel Nov 26 '18 at 5:47
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Plausible, but under-researched.

Lawrence Berkeley National Laboratory has this to say about UV germicidal irradiation (UVGI):

There have been few published studies of the health benefits of applying UVGI systems in ducts of HVAC systems outside of health care facilities. In a study within three office buildings [50], UVGI systems were turned on and off multiple times while not informing occupants. Work related self-reported acute health symptoms were assessed using questionnaires. There were statistically significant 20% to 40% decreases in symptoms during periods of UVGI system operation.

The study referenced as "[50]" is Effect of ultraviolet germicidal lights installed in office ventilation systems on workers' health and wellbeing: double-blind multiple crossover trial as published in The Lancet in 2003.

To briefly restate its conclusions (while adding my own emphasis):

On the basis of within-person estimates, use of UVGI was associated with significantly fewer work-related symptoms overall (adjusted odds ratio 0·8 [95% Cl 0·7–0·99]), as well as respiratory (0·6 [0·4–0·9]) and mucosal (0·7 [0·6–0·9]) symptoms than was non-use.

Finally, Berkeley Lab concludes:

In summary, studies of the health benefits of applying UVGI systems have inconsistent results. Also, there have been very few studies of UVGI in HVAC systems outside of health care facilities.

  • From something as trivial as preventing pathogens from actually going from your duct intake into the room's conditioned air, I'm not surprised that the best they can claim is plausible. Even assuming it's completely effective; I have my doubts that many people get sick through supply duct air compared to just human contact; and air being circulated between people once it's in a room. – JMac Nov 26 '18 at 20:17
  • @JMac, I think they're on to something. It's probably not more than 30 seconds from the air return through the heating unit and back through the ducts--- would you expect a sneeze to settle out 100% in that amount of time? Also, the "very few studies" only applies in non-hospitals. The benefits in hospitals are presumably... well... what do those studies say? – elliot svensson Nov 26 '18 at 23:12
  • @elliotsvensson It seems like hospitals are recommended to employ the "UV-C everything if it's high risk" camp, so it may be pretty effective. I could see it not being as effective in other scenarios though, if you can't really assure enough air changes to eliminate a significant amount of the contaminated air in the timeframe it wouldn't do much. Seems like it's perfect for hospitals, especially things like risk of superbugs. – JMac Nov 26 '18 at 23:37

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