Young surfer wearing sunglasses and mask on a beach.
Sunshine is vital to your health. Most famously, skin cells use the energy in solar radiation to make Vitamin D, which is what enables bones to absorb calcium, helps fight depression and lowers your risk of cancer and cardiovascular conditions.
Light also provides protection against disease, including COVID-19. Virologists at the National Institute of Allergy and Infectious Diseases found that, inside the laboratory, the SARS-CoV-2 coronavirus remains stable on everyday materials like metals, plastic and cardboard for several days. But it wouldn’t last anywhere near as long outside.
When researchers at the National Biodefense Analysis and Countermeasures Center exposed SARS-CoV-2 in simulated saliva to artificial sunlight (equivalent to a sunny day), 90% of viruses were inactivated within seven minutes. This result suggests that Coronavirus is less able to survive under the Sun’s rays and that your risk of exposure is significantly lower in outdoor environments.
As the researchers conclude, “these data indicate that natural sunlight may be effective as a disinfectant for contaminated nonporous materials.”
Sunlight could not only serve to sterilize surfaces and prevent infection, it’s also a potential treatment via ‘phototherapy’, an approach that helped reduce the impact of the 1918 flu pandemic caused by H1N1 influenza A virus. Wavelengths of light toward the blue side of the electromagnetic spectrum — between 200 and 300 nanometers — are potent against many bacteria and some viruses.
Ultraviolet light at 254nm is especially effective. Although known as UV-C or ‘germicidal UV’, it doesn’t always kill germs — around that wavelength, the UV radiation is absorbed by genetic material, preventing genes from directing cells to produce proteins. In the case of a virus, damaged DNA or RNA might stop the viral parasite from replicating in its host cell.
A computer model estimated that, during summer, inactivation of SARS-CoV-2 by UV-C in sunlight should be even faster than inactivating influenza A.
Reduction of viral spread through UV-C light.
García de Abajo et al (2020) ACS Nano.
Some scientists advocate using artificial UV-C in indoor spaces such as on public transportation, in elevators, workplaces and schools, and possibly for services like restaurants, which have a high customer turnover. This would help limit the spread of Coronavirus while allowing everyday life to get back to normal following lockdown. In principle it’s a good idea, but what about the practical limitations?
Direct germicidal UV-C light at 254nm is not safe for people, and can damage eyes and skin. Far-UV-C light (207–222nm), on the other hand, would kill germs without causing harm to human tissue. Physicists at the Center for Radiological Research at Columbia University recently showed that far-UV-C is effective against two relatives of SARS-CoV-2 that cause the common cold. Even at low doses, far-UV-C inactivates 99.9% of the viruses in 25 minutes.
Whether it’s artificial UV or natural sunshine then, the future looks bright for using light to help beat COVID-19.