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UV light can kill coronaviruses


When US President Donald Trump suggested ultraviolet light and injections of disinfectant could be used to kill covid-19 in humans back in April, he was roundly criticised, at least for the latter. However, what if he might be right about UV light?

UV light can kill microscopic creatures such as bacteria and viruses by destroying the molecular bonds in their genetic material. But UV light also damages human DNA, causing eye and skin damage and increasing our risk of cancer. However, It turns out there is a specific wavelength of UV light that’s safe for people but capable of killing coronaviruses, both on surfaces and in the air.

UV light — specifically UVC, that’s light with a wavelength between 200–280 nanometres (nm) — works. It’s been used by hospitals and medical facilities for decades to clean personal protective gear, tools, equipment, rooms, and even water. Depending on how it’s deployed, UVC can be especially good at getting into tiny nooks and crannies that are otherwise very hard to sanitise.

There is a problem with using UVC light on people, though. Germicidal UVC light with a wavelength of 254nm is considered to be carcinogenic, causing DNA mutations in our skin and eyes. Hospitals take extreme measures to use it safely.

Two recent studies, reported in Gizmodo, one conducted at the Vagelos College of Physicians and Surgeons at Columbia University Irving Medical Centre in the US and one at Hiroshima University in Japan, have found that a very specific wavelength of UVC light — 222nm — is unable to penetrate the eye’s tear layer or the dead-cell layer of skin, preventing it from reaching and damaging living cells in the human body.

The Columbia University study, published in June, found that even low exposure to 222nm-UVC light was able to kill two common coronaviruses — which cause seasonal colds — that had been aerosolised. Exposure to this UVC light for about eight minutes killed 90% of airborne coronaviruses; it took about 25 minutes of exposure for 99.9% of the viruses to be killed. In mid-September, Hiroshima University confirmed that 222nm-UVC light was effective at killing SARS-CoV-2 — the virus that causes covid-19 — although the tests were done in a more controlled setting. The researchers exposed a viral culture on a polystyrene plate to a 22nm-UVC lamp at a distance of 24cms, which killed 99.7% of the virus in just 30 seconds.

Despite the success, the Japanese team wants more studies using 222nm-UVC light on real-world surfaces and environments. Nevertheless, it’s an exciting discovery, as 222nm-UVC light could theoretically be safely deployed in public places even when people are around.

A viral culture on a polystyrene plate exposed to a 22nm-UVC lamp at a distance of 24cms killed 99.7% of the virus in just 30 seconds.

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