Cleaning your indoor air isn’t as simple as it sometimes sounds. Your indoor air is a veritable smorgasbord of pollutants, from solid particles like dust, mold, and pollen to gases like like carbon dioxide (CO2), formaldehyde, indoor ozone (O3), and volatile organic compounds (VOCs).
That’s not even including airborne biocontaminants like bacteria and viruses that live on almost any surface you can imagine – and many of these can get into your air and be breathed straight into your airways, penetrating respiratory tissue and infecting your entire body.
That’s whyultraviolet (UV)a air purifiers (UV air purifiers) came onto the scene: to address widespread concerns that air purifiers weren’t doing anything about the millions of infectious microbes and viruses that could cause and spread conditions like colds, the flu, and even tuberculosis.
And during the outbreak of the SARS-CoV-2 virus (severe acute respiratory syndrome coronavirus 2) responsible for COVID-19 (a serious respiratory disease, often fatal), UV air purification for the inactivation of airborne viral particles has drawn even more attention as a way to help stop the spread of this deadly pandemic.
UV light disinfection already has a long history in the medical field. Extensive research shows that UV light specifically helps keep dangerous drug-resistant bacteria from spreading hospital-acquired infections (HAI) (1).
But are UV air purifiers worth it for cleaning your indoor air?
Before you rush out to get this “miracle cure” for the last frontier of airborne pollution, it’s worth looking closer at the claims behind UV air purification to understand whether or not it’ll actually do what it says it can do.
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How does UV light “purify” the air?
UV light as used in a UV air cleaner is designed to disinfect potentially infectious living, organic bacteria and inorganic viral material from the air flowing through the purifier.
UV light’s secret weapon against bacteria and viruses? DNA damage – just like UV rays from the sun can damage your skin cells and cause skin cancer, UV light can damage and sometimes destroy the DNA that makes up bacterial and viral matter (2).
There are two main ways that UV light accomplishes this.
First, bacteria are living organisms, and UV light damages their DNA.
When bacterial DNA is damaged, bacteria can’t complete two key reproductive processes known as transcription and replication that allows them to make more bacteria (3).This keeps them from growing, reproducing, and forming enormous colonies throughout your body that are the source of many infectious diseases.
By contrast, viruses aren’t really living – they’re made up of DNA and RNA (ribonucleic acid, a molecule similar to DNA)material that viruses use to invade the DNA strands of living cells, infecting them with their own contaminated viral DNA and making them reproduce that infected DNA in huge quantities.
This is how viral conditions like colds, flu, and measles spread and become so infectious so fast (4).With sufficient contact time, UV light inactivates this DNA and RNA material, stopping them from ever assaulting organic cells.
But do UV air filters actually work?
UV light alone can inactivate infectious biocontaminants like bacteria and viruses to a certain degree – so it should work in an air purifier, right?
But the specific mechanisms of UV air cleaners aren’t as effective as they might sound. Here’s why (5) (6) (7) (8) (9) (10):
- Bacteria and viruses need extended periods of UV light exposure before they’re disinfected, often up to several hours.Air often flows through UV air purifiers too fast for the UV rays to make any difference.
- Some bacteria can regenerate and infect you again even after being disinfected by UV light.
- UV light does nothing for particles.UV light doesn’t destroy particulate matter like PM2.5 and ultrafine particles (UFPs), so most of these dangerous pollutants will still come right through into your air if the particle filtration mechanism isn’t good enough.
- Many UV air purifiers are also ozone generators. Just like ozone in the earth’s atmosphere reacts with UV rays from the sun, the light and heat in some UV air purifiers can also generate heat that turns free-floating molecules of oxygen (O and O2) and water (H2O) into dangerous ground-level ozone (O3).
- UV light can burn your skin and damage your eyes. Even brief UV exposure can cause permanent skin and eye damage as well as cancer.
And it’s worth noting that ozone particles used in some of these UV air cleaners to charge pollutant particles and take them out of the air produce ground-level ozone.
This type of ozone can be extremely toxic – even short-term exposure can cause a cascade of respiratory symptoms, and long-term exposure has been linked to numerous deadly health conditions (11) (12).
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The ABC’s of UV light
Not all UV light is created equal – only certain types are utilized in UV air filters.
Here’s what you need to know: UV light comes in three distinct forms, distinguished by their wavelengths, that each have different effects on organic matter.
UV-A rays are about 315–400 nanometers (nm), the longest wavelength of the three UV ray types with photons (or light particles) that vibrate just a little faster than those in visible light. This type of UV light isn’t typically used in any air purifiers or similar technology.
But over 95% of the rays from sunlight that make it to the surface of the earth fall into this category (13).UV-A rays are the most likely to penetrate through your skin to cause skin damage and cancer with long-term exposure (14).
UV-B rays are a little shorter than UV-A rays at about 280–315 nm. Their photons vibrate even faster than those in UV-A rays, giving them more energy to damage DNA. But because of their shorter wavelengths, most of them don’t pass through the upper layers of the atmosphere.
The small percentage of UV-B rays that do pass through the atmosphere, however, are the ones most directly linked to skin cancer (15).
UV-C light wavelengths measure between 100 and 280 nm. UV-C is the kind of UV light that’s used in most, if not all, UV air purifiers.
These UV rays have the shortest wavelengths and transmit the most energy, giving them a lot of potential to damage and kill tiny microbes and cells – that’s why they’re used in UV air cleaners to kill bacteria and viruses, especially in a form called ultraviolet germicidal irradiation (UVGI) (16).
But UV-C light is also the most dangerous of the three.
Because of its high energy and intensity, even short-term exposure to UV-C light from a UVC air purifier (or UV-C air purifier) can cause damage to your eyes and skin – and the longer you’re exposed, the more severe the damage can be.
UV technology requires significant contact time to “kill” biocontaminants
There’s another major consideration to keep in mind when you think about using UV light for killing viruses and bacteria – it takes a long time for UV light to kill or inactivate even small amounts of airborne pathogens or surface contaminants. The amount of energy and time it takes UV light to destroy viruses and bacteria is measured in millijoules per square centimeter (mJ/cm2), where one joule (1000 millijoules) equals about one second.
And different contaminants require different durations of UV light exposure to be completely eradicated – here’s what the research says about how long it takes UV light to effectively destroy just one square centimeter of some common viruses and bacteria(17) (18) (19):
- Influenza virus: about 6.6 seconds
- E. Coli: about 6.6 seconds
- Staphylococcus aureus: about 6.6 seconds
- Aspergillus mold spores: 8.8 to 33 seconds
- SARS-CoV: around 60 seconds or more
- SARS-CoV-2 (COVID-19 coronavirus): up to 60 seconds
That may not seem like a long time, but when you cough or sneeze, you produce anywhere from 900 to over 300,000 of these kinds of infected particles at a time, potentially filling hundreds of square centimeters of area in the air of a room(20) (21).
And a UVC air purifier needs from 6 seconds up to 1 minute or more just to kill infected particles in just one of these square centimeters. Given that air often passes through an air purifier quickly (spending less than half a second in the air purifier itself), infected particles can fly past UV light largely unscathed and still infectious.
And that’s assuming that your UV air cleaner uses the right wavelength of UV light at a high enough intensity to effectively inactive airborne biocontaminants – but most UV air purifiers that are sold as safe for use at home only generate low doses of UV light, and they may take even longer to kill even smaller amounts of biocontaminants (22).
This means that a UV air filter can take several hours or more to kill or inactivate infected airborne contaminants from the air in a room (assuming that someone doesn’t cough, sneeze, or breathe again and add even more infected particles to the air).
In short, a UVC air purifier may be able to capture and kill or inactive some thousands of these infected particles, but hundreds or thousands of particles can remain in your air for hours before being killed, able to be breathed in and cause infections.
If biocontaminants are “killed” by UV, can they still harm me?
The short answer here is yes.
Unlike typical air purifiers, UV air purifiers don’t actually remove biocontaminants like viruses and bacteria from your air – they inactivate them as they pass under concentrated UV beams, dismantling the molecular bonds that comprise the DNA of these organisms and sending the inactivated DNA back into the air.
But biocontaminants are typically only partially inactivated by UV light, with the potential of coming back to life – a state called viable but nonculturable (VBNC). In a VBNC state, biocontaminants go dormant after UV exposure, but can “wake up” to regenerate again after some time, even at high doses of UV light up to 300 mJ/cm2 (23).
This means that plenty of infectious biocontaminant particles go right back into the air after passing through the UV light – some are inactivated and harmless, but many are still actively infectious or can become infectious again.
And the level of biocontaminants “killed” by UV light depends largely upon several critical factors in the design of the UV mechanism used in the UVC air cleaner itself.
In general, it’s believed that 40 mJ/cm2 of UV light at a wavelength of 0.254 microns (commonly used in UV air purifiers) can kill up to 99.99% of almost any airborne biocontaminant (24).
But viruses in particular have been shown to need a much wider spectrum ranging from 0.2 to 0.315 microns for effective inactivation—different wavelengths are effective for different types of viruses due to the specific interactions of UV light with various viral DNA proteins—in addition to requiring several seconds of exposure for any level of inactivation.
So even in theory, a UVC air purifier needs a specific wavelength and a specific amount of exposure time to even partially inactivate airborne biocontaminants – it’s not one size fits all.
And in practice, most UV air filters don’t meet the proper wavelength and exposure requirements to sufficiently protect you from the most dangerous viruses and bacteria. You’d need a perfect storm of the right UV wavelength, sufficient exposure time, and the use of other air filtration technologies for UV air purification to truly remove biocontaminants from the air.
Should I get a UV air purifier?
No. Don’t buy a UV light air purifier or any air purifiers that use UV light as a key part of their purification mechanism. It’s dangerous and doesn’t work that well, especially without the use of other proven air filtration methods.
UV disinfection simply doesn’t work at the velocity that air needs to be pulled through a purifier to filter pollutants. Bacterial and viral matter need to be exposed to UV light for a certain amount of time, sometimes as long as several hours at a time, so a few seconds or less under a UV light, no matter how strong, won’t do much to remove microbial pollutants.
UV light somewhat disinfects but doesn’t purify air, and research shows that UV’s disinfection potential for air may be exaggerated.
What should I do to clean my air?
Here are some time-tested and proven tips for improving indoor air quality that don’t rely on ineffective technologies.
Use a high-efficiency room air purifier
For typical rooms that are several hundred square feet or so, a room air purifier like the HealthPro Plus can remove up to 99.5% of pollutants down to 0.003 microns (10 times smaller than the average bacterium or virus) several times an hour, far outperforming UV or standard HEPA air purifiers.
A room air purifier is recommended for spaces like bedrooms, home offices, kitchens, home gyms, and other spaces where you spend a lot of time and need the purest air possible for restful sleep, unhindered cognitive function, or peak physical performance.
Use a whole-house air purifier
Concerned about air quality throughout your household? A UV light air purifier for heating, ventilation, and air conditioning (HVAC)systems isn’t the solution – a high-performance whole-house air filtration system is much more effective.
The Perfect 16 whole-house air purifier fits into your home’s existing HVAC units to draw in air, purify it of up to 96.7% of particulate pollutants down to 0.3 microns and up to 85% of particles down to 0.003 microns with over 170 square feet of filter media, and recirculate the air through your home’s supply ductwork at up to 2,000 cfm so that every room in your home has fresh, clean, medical-grade air.
A whole-house air purifier takes up no space, adds no noise to your HVAC operation, and reduces your electricity bill through patented Advanced Microfiber (AMF) technology that maximizes filter surface area for pollutant removal while reducing air resistance so that purification is easy on your HVAC fan motor.
Use a personal air purifier
Need high-efficiency air purification on the go? The Atem 5-in-1 personal air purifier directs clean air into your breathing zone for instant clean air wherever you need it.
Air quality can be unpredictable, and typical portable “air purifiers” often use dangerous ionization or UV technology that does little to clean the air in your workspace, your car interior, or next to your bed.
The Atem uses HyperHEPA filtration technology to remove up to 99% of particles down to 0.003 microns from the air you’re breathing right now, virtually eliminating pollutant particles without creating harmful byproducts like ozone.
An optional HyperHEPA Plus filter uses an additional layer of activated carbon to remove over 250 types of gases from ambient indoor and outdoor air, including chemicals and compounds like formaldehyde that originate from off-gassing of building materials and upholstery.
UV light can help provide an additional layer of defense against viruses, bacteria, and microbes in the air and on surfaces.
But due to the length of exposure and intensity required to effectively kill airborne biocontaminants, UV light is generally ineffective in air purifiers available for homes and works best in controlled medical environments.
According to the Centers for Disease Control and Prevention (CDC), UV air purifiers, whether they’re called ultraviolet air purifiers, UVC air purifiers, or UV-C air purifiers (or filters or cleaners), can be used as part of an air purification strategy, but shouldn’t be relied on as a sole measure of airborne biocontaminant control (25).
High-efficiency air purification with dense filtration material that can capture the tiniest airborne biocontaminants and pathogens, such as viruses and bacteria, is much safer, more effective, and more reliable than UV air purifiers.
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