Sunlight Kills Coronavirus Quickly, Says Top DHS Official

Coronavirus can be destroyed by ultraviolet rays from the sun, a top U.S. official 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.

Correction 04/27 05:21 a.m.: The headline and article has been corrected to say William Bryan is an official, not a scientist.

William Bryan
William Bryan, head of science and technology at the Department of Homeland Security. Bryan said solar light appears to have a "powerful effect" on killing SARS-CoV-2. Drew Angerer/Getty Images

Centers for Disease Control and Prevention Advice on Using Face Coverings to Slow Spread of COVID-19

  • CDC recommends wearing a cloth face covering in public where social distancing measures are difficult to maintain.
  • A simple cloth face covering can help slow the spread of the virus by those infected and by those who do not exhibit symptoms.
  • Cloth face coverings can be fashioned from household items. Guides are offered by the CDC.
  • Cloth face coverings should be washed regularly. A washing machine will suffice.
  • Practice safe removal of face coverings by not touching eyes, nose, and mouth, and wash hands immediately after removing the covering.

World Health Organization advice for avoiding spread of coronavirus disease (COVID-19)

Hygiene advice

  • Clean hands frequently with soap and water, or alcohol-based hand rub.
  • Wash hands after coughing or sneezing; when caring for the sick; before, during and after food preparation; before eating; after using the toilet; when hands are visibly dirty; and after handling animals or waste.
  • Maintain at least 1 meter (3 feet) distance from anyone who is coughing or sneezing.
  • Avoid touching your hands, nose and mouth. Do not spit in public.
  • Cover your mouth and nose with a tissue or bent elbow when coughing or sneezing. Discard the tissue immediately and clean your hands.

Medical advice

  • Avoid close contact with others if you have any symptoms.
  • Stay at home if you feel unwell, even with mild symptoms such as headache and runny nose, to avoid potential spread of the disease to medical facilities and other people.
  • If you develop serious symptoms (fever, cough, difficulty breathing) seek medical care early and contact local health authorities in advance.
  • Note any recent contact with others and travel details to provide to authorities who can trace and prevent spread of the disease.
  • Stay up to date on COVID-19 developments issued by health authorities and follow their guidance.

Mask and glove usage

  • Healthy individuals only need to wear a mask if taking care of a sick person.
  • Wear a mask if you are coughing or sneezing.
  • Masks are effective when used in combination with frequent hand cleaning.
  • Do not touch the mask while wearing it. Clean hands if you touch the mask.
  • Learn how to properly put on, remove and dispose of masks. Clean hands after disposing of the mask.
  • Do not reuse single-use masks.
  • Regularly washing bare hands is more effective against catching COVID-19 than wearing rubber gloves.
  • The COVID-19 virus can still be picked up on rubber gloves and transmitted by touching your face.