Why You Should Learn About UV Light

The persistence of antibiotic resistant organisms, combined with the recent coronavirus pandemic, has meant that individuals are searching for more innovative ways to stop the spread of microorganisms amongst the population. Recently, products containing Ultraviolet (UV) light, such as UV lights and lamps, have been gaining a lot of traction. Numerous studies have shown that certain types of UV light can be effective at inactivating bacteria and viruses, including human coronaviruses. So how does UV light work to kill viruses and bacteria? and which type of UV light is most effective at doing this?

Woman washing her hands

Looking back in history, in 1903 Niels Ryberg Finsen won the Nobel Prize in Physiology or Medicine for his contribution to the treatment of diseases using concentrated light radiation. Since then, UV radiation has been used to treat diseases such as eczema, vitiligo, and lupus vulgaris. UV disinfection lamps have also been used in hospitals to reduce the transmission of microorganisms that linger in the air of communal treatment rooms. The UV light spectrum is divided into a number of bands which gives rise to different types of UV rays (UVA, UVB and UVC rays), each of these bands will have varying effects on humans and other organisms. UVA rays have the longest wavelengths and account for around 95% of the UV radiation that reaches the earth’s surface. UVA rays are responsible for the tanning effect as these rays from the sun can penetrate the deep layers of the skin. In contrast, UVB rays can only penetrate the surface layers of the skin. UVC radiation from the sun does not reach the earth’s surface at all as it is completely filtered by the ozone layer in the atmosphere. The only way that we are exposed to UVC rays is through artificial sources such as UVC lamps.

Person lying down, getting teeth cleaned

UVC rays have the shortest wavelength and therefore highest energy, which makes them effective at killing bacteria and viruses. When used in appropriate doses, UVC rays can kill microorganisms without damaging surrounding healthy human tissues. One way this works is that UVC light damages the genetic material in the nucleus of the microorganism (bacteria, viruses, fungi). In particular, the UVC light is absorbed by the nucleic acids (DNA and RNA) of the microorganism. The nucleic acid DNA contains a nitrogen base which when exposed to the UVC combines with other bases to form a dimer. This dimerisation prevents the nucleic acid (DNA or RNA) from replicating, therefore stopping the microorganism from surviving. One of the nitrogen bases only found in DNA is called thymine and this molecule is particularly known to form dimers under UVC light. As UVA and UVB light can reach the earth’s surface from the sun, bacteria and viruses have learnt to adapt to these rays, and so they are less effective at killing microorganisms.

UVC sterilizing light on a closet of hotel towels

Most recently, UV light has gained attention due to its effectiveness against human coronaviruses. A paper recently published in Nature, one of the world’s most prestigious academic journals, revealed that Far-UVC light with a wavelength of 200nm can majorly reduce the level of airborne coronaviruses in public spaces. The study used an aerosol irradiation chamber to measure the efficacy of far-UVC light against two human coronaviruses. As mentioned before, the UV light spectrum is divided into a number of bands. In addition to this, UVC light is also divided into separate sub-groups. Germicidal UV light typically has a wavelength of 254nm and is used to disinfect water, air and surfaces, as well as kill bacteria and viruses. The problem with germicidal UV light however is that it can cause burns to the skin and eyes if used directly, so should be used in empty rooms. Far-UVC light on the other hand occupies the wavelengths between 207-222nm and cannot penetrate the skin, but can still inactivate viruses and bacteria. This means it can kill microorganisms potentially without causing harm to healthy human tissues. The study using 222nm Far-UVC light concluded that low dosage UV-C lamps could be deployed in public places such as restaurants and schools to reduce the spread of airborne viruses. Furthermore, as many human coronaviruses have a similar genomic size, it is likely that Far-UVC light will have a similar efficacy against many different types of coronaviruses including Sars-Cov-2 (Covid19).

When used in appropriate doses, UV light serves as a safe and inexpensive tool for reducing the spread of airborne viruses. This type of technology has the potential to be utilised in public places such as hospitals, restaurants, hotels, schools and public transport to reduce the risk for those most vulnerable. The pandemic may also encourage further research to be carried out in this area which may result in advances in the field and new UV treatments for other life-threatening diseases.

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