UVC radiation is a known disinfectant for air, water and non-porous surfaces. UVC radiation has been used effectively for decades to reduce the spread of bacteria, such as tuberculosis. For this reason, UVC lamps are often referred to as "germicidal" lamps.
It has been proven that UVC radiation destroys the outer protein coating of SARS coronavirus, which is different from the current SARS-CoV-2 virus. The destruction eventually leads to inactivation of the virus. However, currently there are limited published data on the wavelength, dose and duration of UVC radiation required to inactivate the SARS-CoV-2 virus.
Generally, apart from understanding whether UVC radiation is effective in inactivating specific viruses, UVC radiation also has some limitations on the effectiveness of inactivating viruses.
Direct exposure: UVC radiation can only inactivate the virus when it is directly exposed to radiation. Therefore, due to the blocking of UV radiation by soil (such as dust) or other pollutants (such as body fluids), the inactivation of the virus on the surface may be ineffective.
Dosage and duration: Many UVC lamps sold to households are low-dose, so it may require prolonged exposure to a given surface area to effectively inactivate bacteria or viruses.
UVC radiation is usually used inside air ducts to disinfect the air. This is the safest way to use UVC radiation, because direct exposure of UVC to human skin or eyes may cause harm.
Can UVB or UVA radiation inactivate SARS-CoV-2 coronavirus?
In terms of inactivating the SARS-CoV-2 coronavirus, UVB and UVA radiation are expected to be less effective than UVC radiation.
There is some evidence that UVB radiation can effectively inactivate other SARS viruses (not SARS-CoV-2). However, this is not as effective as UVC, and is more harmful to the human body than UVC radiation, because UVB radiation can penetrate deeper into the skin and eyes. As we all know, UVB can cause DNA damage and is a risk factor for the development of skin cancer and cataracts.
UVA: UVA radiation is less harmful than UVB radiation, but it is also less effective (about 1000 times) than UVB or UVC radiation in inactivating other SARS viruses. UVA is also associated with skin aging and skin cancer risk.