Ultraviolet light has been used to stop pathogens in their tracks for decades. But does it work against SARS-CoV-2, the virus behind the pandemic?

The short answer is yes. But it takes the right kind of UV in the right dosage, a complex operation that is best administered by trained professionals. In other words, many at-home UV-light devices claiming to kill SARS-CoV-2 likely aren't a safe bet.

UV radiation can be classified into three types based on wavelength: UVA, UVB and UVC. Nearly all the UV radiation that reaches Earth is UVA, because most of UVB and all of UVC light is absorbed by the ozone layer, according to the center for diseases control and prevention, And it's UVC, which has the shortest wavelength and the highest energy, that can act as a disinfectant. 

"UVC has been used for years, it's not new," Indermeet Kohli, a physicist who studies photomedicine in dermatology at Henry Ford Hospital in Detroit, told Live Science. UVC at a specific wavelength, 254 nanometers, has been successfully used to inactivate H1N1 influenza and other coronavirus , such as severe acute respiratory virus (SARS-CoV) and Middle Eastern Respiratory Syndrome (MERS-CoV), she said. A study published June 26 to the preprint database medrix from Kohli's colleagues awaiting peer review now confirms that UVC also eliminates SARS-CoV-2. 

UVC-254 works because this wavelength causes lesions in DNA and RNA. Enough exposure to UVC-254 damages the DNA and RNA so that they can't replicate, effectively killing or inactivating a microorganism or virus. 

"The data that backs up this technology, the ease of use, and the non-contact nature" of UVC make it a valuable tool amid the pandemic, Kohli said. But responsible, accurate use is critical. UVC's DNA-damaging capabilities make it extremely dangerous to human skin and eyes, Kohli said. She cautioned that UVC disinfection technologies should primarily be left to medical facilities and evaluated for safety and efficacy by teams with expertise in photomedicine and photobiology. When it comes to a-home UVC lamps, their ability to damage skin and eyes isn't the only danger, Dr. Jacob Scott, a research physician in the Department of Translational Hematology and Oncology Research at Cleveland Clinic, said. These devices also have low quality control, which means there's no guarantee that you're actually eliminating the pathogen, he said.  

"UVC does kill the virus, period, but the issue is you have to get enough dose," Scott told Live Science. "Particularly, for N95 masks, which are porous, it takes a pretty big dose" of UVC-254 nm to eliminate SARS-CoV-2. This kind of accuracy isn't possible with at-home devices