Answer:

Yes, ultraviolet light in the "C" range, also known as UVC, has been shown to kill SARS-CoV-2, the virus that causes COVID-19. However, more research is needed to test UVC on various household surfaces, and to determine how effective consumer products may be when used in the home, rather than under laboratory conditions.

The big challenge with using UV-C light is being sure your UV lamp provides a large enough dose of UVC light to all the surfaces you need to disinfect, such as a mask, phone, or an entire room, and that you are not exposed to the UVC light, as it is dangerous. UVC works fastest and most reliably on non-porous surfaces, but it may be easier and faster, as well as safer, to clean such surfaces with liquid disinfectants. Think of using UV-C light to disinfect an object like using a hair blower to dry an object -- it can take a lot of time, but with UV-C you often won't know when you're done.

Many UV products marketed as "killing 99.9% of germs" may be so weak that you would need to hold them for an hour at different angles just to disinfect a mask. Masks can be more easily disinfected other ways, such as in a washing machine (for cloth masks) or at low temperature in an oven (for N95 masks). 

If you are still interested in using UV light to help protect yourself from coronavirus, here are the things you'll need to know. Further below are our reviews and comparisons of UVC products marketed to consumers.

How UV Light Kills Germs

UV radiation kills viruses and bacteria by damaging their genetic material (DNA and RNA). Of the three main types of UV light, UVC (which has a wavelength range of 200 to 280 nm) is the most effective for inactivating viruses, with the most effect wavelength being about 260 nm (Lytle, J Virol 2005).

In order to be effective, the right "dose" of UVC must be applied. The dose is a function of the UVC intensity or "irradiance" from a specific distance from the object times the number of seconds the object is exposed. Irradiance is measured in milliwatts (mW) per square centimeter (cm2), and the dose of UVC is measured in millijoules (mJ) per square centimeter (cm2) of the object being irradiated. (In scientific terms, 1 mWs/cm2 =1 mJ/cm2).

So if your UVC lamp has an irradiance of 5 mW/cm2 at a specified distance from an object, then holding the lamp at that distance from the object for 8 seconds will deliver a dose of 40 mJ/cm2, because 5 mW/cm2 multiplied by 8 seconds = 40 mWs/cm2 or 40 mJ/cm2.

A dose of 40 mJ/ cm2 is generally considered sufficient to disinfect (99.9% reduction in infectivity) a wide range of bacteria and viruses, including certain coronaviruses that infect animals (Malayeri, IUVA News 2016).

Although sunlight does not contain UVC light (because UVC light is filtered by the earth's atmosphere), it still appears to be effective in reducing the infectivity of SARS-CoV-2. According to preliminary tests funded by the U.S. Department of Homeland Security (DHS), simulated summer sunlight reduced SARS-CoV-2 in aerosolized saliva by 90% within 6 minutes versus 19 minutes in simulated winter/fall sunlight. Compared to no sunlight, the rate of decay of infectivity was 32 times faster with the summer light and 14 times faster with the winter/fall light (Schuit, J Inf Dis 2020). Note, however, that these reductions are not instantaneous: If you immediately inhale droplets from a cough or sneeze of an infected person, it won't matter if you are outside on sunny day or indoors. In addition, researchers in China have reported that high temperature and UV radiation do not appear to reduce the transmission of COVID-19 (Yao, Eur Respir J 2020).

What Dose of UVC Light Kills SARS-CoV-2?

In its published guidance for consumers, the FDA states that UVC radiation has been shown to destroy the outer protein coating of other coronaviruses and "may also be effective in inactivating the SARS-CoV-2 virus," but notes that "there is limited published data about the wavelength, dose, and duration of UVC radiation required to inactivate the SARS-CoV-2 virus."

A laboratory study (not yet peer-reviewed) showed that when pieces of fabric from N95 masks and stainless steel were contaminated with a high concentration of SARS-CoV-2 and then exposed to a large hospital-type UVC lamp (containing a large array of small, LED UVC lamps), it took about one hour for the virus to become undetectable on the mask but just about 12 minutes on steel. The distance from the UVC lamp to the objects was approximately 20 inches (50 cm), at which distance the lamp had an irradiance of just 0.005 mW/cm2 (or 5 microWatts/cm2 or 5 µW/cm2) (Fischer, medRxiv, 2020 — preprint). This means that the effective dose needed to kill the virus to the point of being undetectable on the N95 fabric was 18 mJ/cm2 and, on steel, it was just 3.6 mJ/cm2.

Bear in mind that extra time might be needed to disinfect surfaces of larger objects and those with curved surfaces which would require different lamp angles. Futhermore, as the FDA cautions, "It is important to recognize that, generally, UVC cannot inactivate a virus or bacterium if it is not directly exposed to UVC. In other words, the virus or bacterium will not be inactivated if it is covered by dust or soil, embedded in porous surface or on the underside of a surface..."

Risks of UVC light

UVC light can damage cells in your skin and eyes just as it damages microorganisms, so you need to use it without exposing yourself. The FDA warns you should "never look directly at a UVC lamp source, even briefly."

UVC light devices should never be used to attempt to disinfect hands or skin.

Repeated UVC treatment can gradually decrease filtration efficiency of N95 masks and the rate at which it does so can vary by brand/product; some research suggests that this no more than 9 treatment cycles should be used (Peltier, Infect Control Hosp Epidemiol 2020).

In addition, repeated use of UVC may weaken some components of objects, such as rubber straps on masks.

The FDA also advises that some UVC lamps contain mercury (which is toxic even in small amounts), so extreme caution is needed in cleaning up and disposing of a UV light that has broken.

Be aware that the FDA has expressed risk with using UV light, as well as ozone gas, to clean, disinfect, or sanitize continuous positive airway pressure (CPAP) devices and accessories.

Do UV products sold to consumers work?

As noted above, a UVC sanitizing or disinfecting device should have a stated wavelength between 200 to 280 nm, preferably closer to 260 nm. But just as important, it needs to disclose its irradiance in mW/cm2 (or microW/cm2, written as µW/cm2; 1,000 microW/cm2 = 1 mW/cm2) and the distance at which this can be achieved.

Many products state their wavelength, but few products provide their irradiance, which is needed to determine if they can deliver an effective dose to kill coronavirus in a reasonable amount of time. For example, there is probably no point in buying a UV wand with low irradiance if it means that you'll have to slowly move it over an object for an hour. On the other hand, the higher the irradiance, the greater the risk to your skin and eyes when a light wand or lamp is used.

For home use, UVC "boxes" seem to make more sense than wands and open lamps. These enclosed boxes are designed to disinfect phones or other small solid and generally flat objects, like credit cards, keys, or watches. Porous or non-flat objects may cause shadowing that prevents the light from reaching parts of the object. Because the boxes are enclosed, they are safe to use, and because you can place your phone in the box and walk away, they don't take extraordinary effort. The time needed in these boxes tends to range from about 1 to 10 minutes.

If you are considering purchasing a UVC light device, the FDA suggests the following:
  • Ask the manufacturer about the product's health and safety risks and about the availability of instructions for use/training information.
  • Ask whether the product generates ozone.
  • Ask what kind of material is compatible with UVC disinfection.
  • Ask whether the lamp contains mercury. This information may be helpful if the lamp is damaged and you need to know how to clean up and/or dispose of the lamp.

How do UV products compare?

We have reviewed and profiled several widely sold UVC products, including handheld wands (GermAway and Verilux Clean Wave) and ultraviolet light boxes (PhoneSoap, HoMedics, and 59S).

Sign in or join now to read our reviews and get our Bottom Line opinion about ultraviolet devices and other methods such as ozone generators or air purifiers for disinfecting coronavirus.

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45 Comments

Join the conversation

Evelyn 20405
July 16, 2020

FYI: Ozone and UVL sterilizers
I have KN95 masks purchased from Amazon, made in China, that are listed (but not approved) by the CDC. They tested at 94%+- high and 70% low. I want to be able to reuse them and considered sterilizing them. Then discovered the FDA website warning below:

FDA News Release February 27, 2020
“Today, the U.S. Food and Drug Administration is issuing a Safety Communication to inform patients and health care providers that devices claiming to clean, disinfect or sanitize continuous positive airway pressure (CPAP) devices or accessories (such as masks, tubing, headgear) using ozone gas or ultraviolet (UV) light are not legally marketed for this use by the FDA in the U.S.”

https://www.fda.gov/news-events/press-announcements/fda-reminds-patients-devices-claiming-clean-disinfect-or-sanitize-cpap-machines-using-ozone-gas-or

See also:
https://www.fda.gov/consumers/consumer-updates/cpap-machine-cleaning-ozone-uv-light-products-are-not-fda-approved

d20521
August 7, 2020

I recently did a fair amount of study of ozone generators for destruction of mold and spores. You are wise to find and consider information from the FDA when looking into these things, but it is wiser still to not stop there.

I went on to examine what FDA said, and why. Here, you quote the FDA as warning that ozone and UV devices "are not legally marketed for this use by the FDA in the U.S." This warning just means FDA hasn't approved these devices, it does not mean that they cannot be effective or safe. For example, ozone can be effective for indoor mold remediation, but the necessary concentration is too high to be safe for occupied spaces. The obvious and easy answer is that during disinfection the space must not be occupied. But because adequate disinfection is achieved only with "unsafe levels" of ozone, the FDA will not approve devices for this use.

While selecting from FDA approved devices would be convenient, absence of such a list needn't be the end. With a little legwork one can find good, research based information, and conclude what safe & effective options exist. (CL is a great example of such a source.) Think about your question (what you're trying to achieve), then look for related industry journals, scientific journals, and www.ncbi.nlm.nih.gov/ are other great sources.

Jennifer20257
June 26, 2020

my gym sz they are using UV air sanitizing in the a/c ducts.....is this effective against Covid?

ConsumerLab.com
July 13, 2020

It's possible it can help, but it should be used along with other preventative measures, such as proper cleaning and disinfecting of surfaces and social distancing.

In it's guidelines for employers/owners of office buildings during the COVID-19 pandemic, the CDC suggests when done in according to industry standards, use of ultraviolet germicidal irradiation (UVGI) in HVAC systems can be a "supplemental technique to inactivate potential airborne virus in the upper-room air of common occupied spaces (https://www.cdc.gov/coronavirus/2019-ncov/community/office-buildings.html). The agency refers to the standards set by The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) which recommends installing UVGI into air handlers and/or ventilating ducts where appropriate to help control airborne infectious diseases (https://www.ashrae.org/File%20Library/About/Position%20Documents/Airborne-Infectious-Diseases.pdf).

Kevin20210
June 18, 2020

also...to be added to my previous comment...what I'm considering buying stats are:
irradiation 2500 uw/cm2 and UV wave is 254

Again, just wondering if this is a viable product to get rid of germs on airplane seat fabric-armrests-hotel door knobs...approx. time to irradiate?

TYIA

ConsumerLab.com
June 24, 2020

Given that the wand is held at the distance specified by the manual, that should deliver an effective dose in just a few seconds. However, keep in mind you may have to move the wand over each cm2 section for that amount of time, and effectiveness may vary depending on the type of surface (metal, fabric, etc.).

Kevin20200
June 17, 2020

I'm wondering how effective (and how long it'd have to be held over?) a 3w "wand" would be for:
a) doorknobs
b) seats wi/fabric
c) arm rests

(think plane seats et al)

Tyia

Also, if this would take like an hour or something, then, what wattage would be best for
above?

Alexander19771
May 1, 2020

I have a negative ion generator (Weiner VI-3500) that apparently puts out 3.4 trillion ions per second. Such negative ions neutralize positively charged air pollutants/allergens/germs/viruses. How effective is this in fighting coronaviruses or any viruses for that matter? Thanks

ConsumerLab.com
May 20, 2020

We don't have information on that particular product.

LYNN19760
April 29, 2020

A home shopping channel was selling hand held vacuums with UV light. The claim is that the light kills dust mites, viruses, etc while vacuuming the surface. It's recommended for upholstered furniture, bedding and mattresses, and other soft surfaces. I wonder how long one would have to hold such a vacuum on an area to kill viruses. I don't know how large the light surface is in these appliances. No claims for Covid-19 are being made.

ConsumerLab.com
May 4, 2020

Without knowing the product's irradiance, it's not possible to know if it delivers an effective dose of UVC and for how long you would need to apply it to one small area. However, it would likely be much longer than the normal, quick pass used with hand held vacuums. Also, keep in mind that UVC works best on hard, non-porous surfaces and may be less effective on softer, more porous surfaces like fabric.

H A19726
April 28, 2020

As a follow-up to my earlier question, I suggest your review of the studies done at Columbia University and papers by: DAVID J. BRENNER,
CENTER FOR RADIOLOGICAL RESEARCH, Columbia University.

H A19725
April 28, 2020

Have you reviewed the new claims regarding "Far UV" light for sterilizing? It is claimed that this UV spectrum sterilizes in a few seconds.

ConsumerLab.com
May 14, 2020

The preliminary research on far-UVC light does look promising, but further independent studies are needed to confirm this. Even if safe, there are many design and engineering issues to be worked out to determine the best way to deploy such devices.

James19921
May 16, 2020

Are you familiar with this February 2018 study? "Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases," D. Welch et al.,
https://www.nature.com/articles/s41598-018-21058-w

ConsumerLab.com
May 20, 2020

Yes, thank you for sharing the link. This is part of the preliminary research we refer to in the comment above.

Kathryn19708
April 27, 2020

I just had a PREMIERone installed in my home. Will that unit offer any protection from coronavirus. It is a MUV-403H unit.

ConsumerLab.com
April 29, 2020

UVC light systems are sometimes used in ductwork in commercial and institutional settings, but they are custom-designed for that purpose and generally use many lamps. In a home setting, you would need to have the right combination of UV lamp power, air velocities, and position of the lamp in the ductwork in order to be effective.

If placed properly to irradiate the air conditioning cooling coils, it may work to keep the coils clean and prevent mold growth during the summer cooling season, when the coils are frequently wet with condensation. If however, the UV light is just placed in the ductwork somewhere, and the air is rushing by in a second or two, the dose that the air receives is potentially much too low to achieve much disinfection of the air.

Jeffrey19705
April 26, 2020

How is this different from any other virus? I hear bleach is effective on this virus too!!!!

ConsumerLab.com
April 27, 2020

Please see our information about bleach and other disinfectants recommended for coronaviruses here https://www.consumerlab.com/answers/heat-to-kill-coronavirus/heat-coronavirus/#disinfectants.

Evangelina19698
April 26, 2020

I have 2 Room Honeywell Air Purifiers that has settings for Allergens and Germ. I have allergies and noticed it helps alleviate my seasonal or dog allergies.

It also has a Germ setting does this have the capabilities of killing the COV19- virus as well?

ConsumerLab.com
April 29, 2020

We don't have enough information about this product to comment on it specifically, but we do note that the EPA advises not relying on air purifiers to protect from COVID-19, as noted above.

Lois19697
April 26, 2020

Who didn't know that sunlight kills COVID-19?? I put my mask out in the bright sunlight to disinfect it. Remember when we put our sheets out in the sunlight on clotheslines to dry them? We did that because the sun naturally bleaches them. The more we think we know....the more we realize we already knew it.

Marsha19692
April 26, 2020

so,if packages are left out in the sun, for even a short time, they would be safe to handle?

ConsumerLab.com
April 29, 2020

There is not enough information at this time to say. While the research using simulated sunlight suggests leaving packages in sunlight could potentially help, differences in temperature, humidity and the shape of the package or item could affect the results.

Elisa19636
April 22, 2020

My Germ Guardian air filter has a UVC light in it that I keep on. I don’t know know if it’s really effective at killing the virus, but there is no reason to not use it. Does anyone know if it really is effective or not?

ConsumerLab.com
April 22, 2020

Hi Elisa - We looked at an image of the product and it's hard to imagine how it can achieve an effective dose of UV. The lamp is apparently at the top of the device, but air flows along the length of it, so the distribution of UV will be weak across most of the airflow cross-section.
Also, generally the air goes by quite quickly so the combination of weak UV plus short time doesn't give much of a dose to be effective. The EPA does not recommend relying on air purifiers to prevent COVID-19. We've added information about this in the answer above.

Hans19657
April 22, 2020

What about a Molekule air filtration unit?

ConsumerLab.com
April 23, 2020

We have not reviewed this product, but according to the company's website, the FDA has granted 510(k) Class II Medical Device Clearance for the Molekule Air Pro RX, a device intended use in medical care settings to destroy bacteria and viruses in the air. The company states its tests showed this device "destroyed 99.9994% of RNA virus MS2 on the filter in 24 hours, which is a proxy for SARS-CoV-2, the virus that causes COVID-19."

The website states its home devices also removed 99.99% of MS2 when tested in a small chamber. Again, we have not reviewed this product or the company’s data, but a list of criteria used for FDA 510(k) Class II Medical Device Clearance during a public health emergency can be found here https://www.fda.gov/media/136533/download.

Elisa19684
April 24, 2020

Thank you for looking at it. I was definitely dubious of the short amount of time the molecules would be in contact with the uvb light.

Vicki19700
April 26, 2020

Now I am worried that the light on the Germ Guardian is dangerous, could you comment more on this, please?

ConsumerLab.com
April 27, 2020

It's important not to exposure your eyes or skin to UVC light. Please see "Risks of UVC Light" above.

Joseph19634
April 22, 2020

Thanks for this!

Verilux also offers (offered?) a presumably more powerful, less portable version (https://www.bedbathandbeyond.com/store/product/verilux-reg-cleanwave-uv-c-sanitizing-wand/1015860065), which we retain, within which the U/V light still works. it has a neat safety feature that turns off the light if the wand is inverted (facing up).

Anyway - one wonders how this item would fare for use with a mask...

Jeffrey19593
April 20, 2020

Very helpful. Couldn't find this information anyplace else.

Earl19571
April 20, 2020

Have you reviewed CPAP disinfecting machines, both UVC (e.g. Lumin) or Ozone?

ConsumerLab.com
April 23, 2020

We have not reviewed CPAP sterilizers, but we've add some information about these in the answer above.

Janet19856
May 10, 2020

Please consider this a request that you put CPAP sterilizers on your To Do list for future reviews!

ConsumerLab.com
May 11, 2020

Although a good question and worthy of research, this is outside our area of focus at this time.

Nicholas19541
April 19, 2020

Wondering about CPAP UV sterilizers like the lumen, https://www.cpap.com/productpage/3B-medical-lumin-uv-cpap-sanitizer

ConsumerLab.com
April 22, 2020

Hi Nicholas - We've added information about CPAP UV sterilizers in the answer above.

Marthe20153
June 10, 2020

I don't see the information you posted about CPAP machines. Could you please send me a link? Thank you!

Gail19533
April 19, 2020

What about sunlight?

ConsumerLab.com
April 27, 2020

We've added information about sunlight in the answer above.

Brad19525
April 19, 2020

What about sunlight? I would expect that by placing an object outside in sunlight would have a significant effect. Later in the year when temperatures rise, direct sunlight would warm the material likely providing an enhanced effect in combination with the natural UV light.

ConsumerLab.com
April 27, 2020

Please see the information about sunlight we've added to the answer above.

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