Ultraviolet Germicidal Irradiation and COVID-19

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In the 2020 COVID-19 pandemic, extreme shortages of personal protection equipment (PPE) have been a major issue for medical workers and home caregivers. Even the Centers for Disease Control and Prevention (CDC) recognize the problem, publishing guidelines for the extended use and limited reuse of disposable face masks and other materials.

I recently wrote about a Chinese study that evaluated different ways to “disinfect” used N95 masks. They concluded that oven dry heat at 70 degrees Celsius (about 160 degrees Fahrenheit) for 30 minutes maintained the physical integrity of the mask as well as the 95% filtration efficiency.

This same study evaluated ultraviolet germicidal irradiation (UVGI) and considered it likely to be effective as well.  They stopped short of recommending this method, however, because they didn’t have the technology to measure viral particles on the masks after exposure.


UV light has long been considered to be lethal to viruses. It works by damaging viral DNA or RNA; most viruses have one or the other, but not both. With a damaged genetic code, replication is more difficult and most viruses are deactivated. I hesitate to say “killed”, because it’s really not certain whether viruses technically meet the definition of life.

With commercial sanitizers and disinfectants in scarce supply, UV irradiation is being used more and more to sterilize PPE, instruments, and entire rooms.

There aren’t a lot of university studies yet that prove UV light specifically deactivates SARS-CoV2. We do have evidence that UV light deactivates its relatives, SARS-CoV1 (Sudden Acute Respiratory Syndrome) and MERS (Middle East Respiratory Syndrome). Since UVGI seems to be effective against SARS-CoV2’s close relatives, it’s no surprise that the CDC endorses its use in the current pandemic as well as against other airborne viral particles.


Not just any UV radiation will do. Sunlight contains different types of UV light. Three main types are:

UVA:  The vast majority (95%) of UV radiation reaching the surface of the planet, it’s capable of penetrating deeply into skin to the dermis. It’s considered to the main cause of age-related skin changes, such as wrinkles and spots. 

UVB: UVB comprises close to 5% of UV radiation to which we are exposed. Although reaching only the top layers of skin, damage to skin DNA can lead to sunburns and skin cancers. Protection from UVA and UVB radiation can be obtained with the proper use of sunblock.  

Note: UVA and UVB exposure, as well as their effects, can also occur with the use of “tanning beds”.

UVC: UVC radiation is a shorter, higher-energy wavelength than UVA and UVB. It’s good at damaging the genetic material of both viruses and humans. While UVB may take hours to cause sunburn, UVC may take only seconds to do the same damage. Fortunately, it’s rare to encounter it, thanks to the filtering capability of our ozone layer.


Although little natural UVC radiation reaches us, many artificial sources of UVC have become a method of disinfection in hospitals, factories, and even airplanes. Stand-alone UVC lamps are used to regularly sanitize entire rooms in a relatively short period of time. On a one-time basis, these items can be used to disinfect a hospital room before a new patient occupies a bed or even the home sick room.

If you don’t have to sterilize an entire room, UVC wands and sterilization chambers are available to treat instruments and some personal protection equipment. A laptop keyboard may take less than 10 seconds to sanitize; a mattress may take up to four minutes.

UVC radiation is also a way to rid drinking water of certain microbes which are resistant to chlorine treatments, such as cryptosporidium.

Used face masks are now being disinfected in many medical centers’ biosafety cabinets. Smaller units available for the home disinfect certain items in 15 minutes. There are some risks: Be aware that skin or eye exposure, even for a short time, may lead to cancers or cataracts.


A study in the periodical “Nature” recently described a type of UV known as “Far-UVC”. Far-UVC is an even shorter wavelength that, so far, appears to inactivate microbes without harming human skin. It can, however, go deep enough to eliminate bacteria and viruses on the skin and other surfaces. 

One study on Far-UVC showed that it can kill airborne flu viruses. If further research agrees with preliminary data, vehicles and other indoor environments may one day become Far-UVC chambers.

UVC lamps currently on the market, however, don’t use Far-UVC. Most germicidal UV lamps are mercury vapor lamps that emit energy at a wavelength of 253.7 nanometers (near the maximum germicidal level). They may be used to irradiate air in ductwork to disinfect it before recirculation; alternatively, irradiating air at upper levels of rooms is accomplished with UV lamps mounted on the walls or suspended from the ceiling. In the latter, the germicidal effect depends on air mixing between lower and upper levels of rooms via convection.

Can UVA or UVB work to disinfect items? The World Health Organization recommends using direct sunlight for 6-8 hours to disinfect water in a clear container. The UVA in sunlight reacts with dissolved oxygen in water to produce hydrogen peroxide, the active ingredient in many household disinfectants. Without water, sunlight will still help clear surfaces of microbes, but it takes much longer.


Despite its potential, Far-UV irradiation doesn’t penetrate porous fabrics like bedding and upholstery.

UVGI is not recommended as a substitute for HEPA filtration, local exhaust of air to the outside, or negative pressure. This is especially true if the air from the rooms of infected patients must recirculate to other areas of a medical facility.  The use of both UV lamps and HEPA filtration in a single unit seems to offer little additional benefit over HEPA filters alone.

Still, UVGI has potential for both airborne virus deactivation and eliminating viruses on surfaces. This makes it useful for COVID-19 or other respiratory infection outbreaks. In the end, the effect varies by wavelength, organic matter, temperature, type of microbe, distance of the light from the object to be disinfected, shadowed areas, and even dirty lamp tubes.

Despite current limitations, UVGI has a great deal of potential in a post-pandemic world. As we learn more about its effect on both germs and humans, UVGI may stop some outbreaks in their tracks and save a lot of lives.

Joe Alton MD

Dr. Alton

Learn more about contagious viral diseases in our latest book “Alton’s Pandemic Preparedness Guide”, available at Amazon or at store.doomandbloom.net

Hey, don’t forget to check out our entire line of quality medical kits and individual supplies at store.doomandbloom.net. Also, our Book Excellence Award-winning 700-page SURVIVAL MEDICINE HANDBOOK: THE ESSENTIAL GUIDE FOR WHEN HELP IS NOT ON THE WAY is now available in black and white on Amazon and in color and color spiral-bound versions at store.doomandbloom.net.

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