COVID-19: Disinfection with ultraviolet light poses risks: doctor

Disinfection products that use ultraviolet light are increasingly popular amid the COVID-19 pandemic, but people should be aware of the product’s potential health risks, a doctor said on Friday.

Yen Chun-yu (顏俊宇), a pediatrician at Taipei Veterans General Hospital, wrote on Facebook that many people have asked him about devices emitting ultraviolet light with wavelengths of 100 to 280 nanometer to sanitize surfaces.

However, there is no scientific evidence that light in that wavelength bracket kills SARS-CoV-2, the virus that causes COVID-19, he said, adding that the light might damage the DNA of microorganisms, including bacteria, viruses and fungi.

The sun also emits those wavelengths, but they are mostly absorbed by the ozone layer in the Earth’s upper atmosphere, Yen said, adding that sunlight has no disinfecting qualities, as evidenced by sunnier countries hit hard by the pandemic.

Ultraviolet light with longer wavelengths, which can penetrate the atmosphere, can cause tanning, sunburn and even skin cancer, he said.

Light with a wavelength of about 254 nanometer is most commonly used for disinfection, Yen said, adding that this wavelength, applied at 15.54 milliwatts per cm2, can kill most bacteria within one minute.

Light with a wavelength of 207 to 222 nanometer has a less damaging effect on human skin and eyes, he said.

Disinfection lamps using those wavelengths might cause light damage to the skin and eyes, but seldom cause skin cancer or cataracts, Yen added.

Ultraviolet light cannot penetrate dust, soil or bodily fluids, while paper, glass or fog largely reduce its intensity, Yen said, adding that it has to be applied directly to a relatively even surface to kill microorganisms.

People should not apply the devices to their skin and not leave the room when the lamp is in use to disinfect surfaces, he said.

To achieve the best results, the lamps should be applied for 30 minutes to an hour, he said.

Ultraviolet light of shorter wavelengths is used to synthesize ozone, or trioxide, from oxygen, Yen said, adding that ozone can also be used for disinfection.

However, excessive exposure to the gas might cause respiratory conditions including asthma, he said, adding that exposure over eight hours to more than 0.1 parts per million ozone in an indoor setting is dangerous.

People should leave the room while applying a device that synthesizes ozone for disinfection, only use such devices in well-ventilated settings and only return to the room 30 minutes to an hour after the device has been switched off, Yen said.

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