In recent years, the internet has been teeming with information on “health”. Among these, the concept of disinfecting clothing and other objects with ultraviolet (UV) light has become extremely popular.
UV rays
Since its discovery in 1878, artificially produced ultraviolet C (UVC) radiation has become an essential sterilization method. It finds its applications in hospitals, aircraft, offices, and factories on a daily basis. UVC light is also fundamental to the sanitization of drinking water. During the process, some parasites may grow resistant to chemical disinfectants such as chlorine, so UVC provides a failsafe.
Ultraviolet germicidal irradiation (UVGI) is a method that incorporates ultraviolet C or UVC light to kill or inactivate microorganisms. It achieves this by destroying microbial nucleic acids and disrupting their DNA, thereby inactivating their ability to perform vital cellular functions.
Sunlight contains 3 types of UV light:
UVA, which makes up most of the ultraviolet radiation reaching the Earth’s surface. It can deeply penetrate the skin. UVA is considered to be responsible for causing up to 80% of skin aging, from wrinkles to age spots.
UVB, which can destroy skin DNA, leading to sunburn and eventually skin cancer.
Both UVA and UVB, are well-known forms of UV light and can be blocked by using good sun creams. However, UVA and UVB can damage the skin, but not to an extent as UVC.
UVC is an obscure part of the spectrum that consists of a shorter and more energetic wavelength of light than UVA and UVB. It is especially efficient at destroying genetic material in humans and viral particles. Luckily, most of us are unlikely to have ever encountered any UVC. The reason behind this is that UVC is filtered out by ozone in the atmosphere long before it reaches our fragile skin.
Otherwise, the scientists would have figured out ways to harness UVC to kill microorganisms.
Although no research has been conducted on evaluating how UVC affects Covid-19 specifically, studies have shown that it can be used against other coronaviruses such as SARS. The UVC radiation warps the structure of the genetic material of these viruses. Furthermore, it prevents viral particles from multiplying. The use of UVC may not be as good as we might have hoped. A recent study assessing whether UVC could be used to disinfect PPE revealed that while it is possible to kill the virus with UVC, one experiment showed the requirement of the highest exposure out of hundreds of viruses that have been studied. Factors including the shape and type of surface material decided the quantity of UV light needed. Concentrated UVC has been made available for combatting against Covid-19. Moreover, there has been an increase in UV equipment sales and supplies. But there’s a major caveat.
UVC is hazardous which is why you should avoid its exposure. It can take hours to get sunburn from UVB, but with UVC it is a matter of seconds. For safe use of UVC, you need specialist equipment and training. The World Health Organization (WHO) has strictly warned people against using UV light to sterilize their hands or any other part of their skin.
Scientists have discovered a new kind of UVC that shows great promise and is less hazardous to handle, but lethal to viruses and bacteria: far -UVC Far-UVC has a shorter wavelength than regular UVC, and until now, experiments with human skin cells in the lab have shown that it doesn’t damage their DNA. Further research is needed to confirm this. On the other hand, bacteria and viruses are not easily removed because they are too small for the light to penetrate them. A study found that UVC can prevent mouse wounds from becoming infected with the superbug MRSA. Whereas, another research reported that it can kill flu viruses suspended in the air.
The majority of the UVC lamps available in the market do not use far-UVC. It has been tested on human and animal cells in petri dishes, but is yet to be tested on humans. Thus, we can understand that this type of UV radiation probably will not be of help during the current pandemic.
Can Sunshine be a solution towards COVID-19?
Would UVA or UVB work? And if so, does that mean you can disinfect things by leaving them out in the sun?
The short answer is: maybe – but it may not be a reliable solution.
Sunlight is a popular means of sterilizing water; the World Health Organization (WHO) also recommends this practice. In this technique, water is simply poured into a glass or plastic bottle and kept out in the sun for six hours. It is thought to work because the UVA in sunlight reacts with dissolved oxygen in the water to produce unstable molecules such as hydrogen peroxide (H2S). H2S is the active ingredient in many household disinfectants since it can destroy pathogens.
Sunlight would serve useful in disinfecting surfaces even in the absence of water, but it may take a longer time than estimated.
Scientists have found that flu cases in Brazil tend to rise in the presence of smoke, which dilutes UV. The problem is we are unaware of the duration because it is early to declare findings from a large number of studies on the new coronavirus strain. According to researchers, when the virus gets suspended in the air, its half-life (the time taken to deactivate half the particles in a particular sample) in “ordinary conditions” (20% humidity and a temperature of 70-75F (21.1-23.9C)) is around an hour. It must be noted that when sunlight is added into the equation, the half-life drastically reduced to one and a half minutes.
Research information to date have been alluded to in the briefing and a leaked report, implying that they have not been officially published or peer-reviewed. It remains unclear as to what wavelength or intensity of light was used in the studies. It is, therefore advisable to view the results with caution until they have been examined properly.
In the meantime, we can gain insight from research on other viruses.
For example, research on the SARS virus, which is closely related to covid-19, declared that exposing the virus to UVA for 15 minutes had no impact on how its pathogenicity. The study had a limitation; it did not consider exposures for longer durations, or exposure to UVB that is known to be more damaging to genetic material than UVA.
Another study found that if flu particles are exposed to sunlight for long durations and if the sunlight intensity is great, then they may be less infectious. The only drawback of the research was that it analyzed flu suspended in the air, rather than dried onto objects.
No one knows how long it takes to deactivate covid-19 using sunlight, or the sunlight intensity required for the process. In other words, disinfecting surfaces with sunlight can pose problems.
Hence, it is understood that disinfecting your skin with any kind of UV will lead to damage and increase your risk of skin cancer. Also, once covid-19 enters your body, any quantity of UV light will fail to impact your health, irrespective of whether or not you are infected with the virus.
