Sunlight Kills Coronavirus Quickly, Says Top DHS Scientist

Coronavirus can be destroyed by ultraviolet rays from the sun, a top U.S. scientist announced at a briefing from the White House coronavirus task force Thursday. William Bryan, science and technology advisor to the Department of Homeland Security (DHS) secretary, said in a press briefing that sunlight has a significant impact on the pathogen.

“Our most striking observation to date is the powerful effect that solar light appears to have on killing the virus, both surfaces and in the air,” he said. “We’ve seen a similar effect with both temperature and humidity as well, where increasing the temperature and humidity or both is generally less favorable to the virus.”

The study, carried out at the National Biodefense Analysis and Countermeasures Center in Maryland, which is part of the DHS, has not yet been made public and is awaiting external evaluation.

There are three types of ultraviolet (UV) light given off by the sun, known as A, B and C. UVA and UVB are common types of wavelengths emitted from the sun. However it is UVC—a subtype of ultraviolet light—that destroys genetic material in humans and in viral particles and is therefore able to inactivate microbes.

UVC is filtered out by ozone in the atmosphere before it reaches our skin, otherwise it would cause damage. Artificially-created UVC has become a standard way to sterilize objects in hospitals, airplanes and factories.

In the briefing, Bryan summarized the findings of the experiment, which showed that the virus’s half-life was 18 hours when the temperature was 70 to 75 degrees Fahrenheit, with 20 percent humidity on a non-porous surface.

However, the half-life dropped to six hours when humidity rose to 80 percent. It fell again to just two minutes when sunlight was added to the experiment.

The research poses several questions, including the intensity and wavelength of the UV light used in the experiment. It is also not known whether it imitates actual natural sunlight in the warmer months either.

Although the study suggests the virus survives for a shorter period in sunlight, Bryan said the findings are not an excuse to ignore stay-at-home orders. “It would be irresponsible for us to say that we feel that the summer is just going to totally kill the virus and then if it’s a free-for-all and that people ignore those guides,” he said.

The World Health Organization also warns against using ultraviolet disinfection lamps to sanitize hands or other areas of the skin, as even brief exposure to UVC light can cause burns and eye damage. In addition, the WHO warns that exposing yourself to temperatures higher than 77 degrees Fahrenheit does not prevent you from contracting COVID-19.

Studies have shown that ultraviolet light can be used against other coronaviruses such as SARS, as the radiation prevents the viral particles from replicating themselves. However, scientists are only just beginning to study the impact of UV light on the novel coronavirus.

Earlier this month, researchers at University of California Santa Barbara announced they were developing ultraviolet LEDs that have the ability to decontaminate surfaces—and potentially air and water—that have come in contact with the new coronavirus.

“One major application is in medical situations—the disinfection of personal protective equipment, surfaces, floors, within the HVAC systems, et cetera,” materials doctoral researcher Christian Zollner said in a statement. “UVC light in the 260 to 285nm range most relevant for current disinfection technologies is also harmful to human skin, so for now it is mostly used in applications where no one is present at the time of disinfection.”

Newsweek has contacted the National Biodefense Analysis and Countermeasures Center for comment.