All about UVC sterilisation
The demand for air purifiers has exploded in recent years due to concerns over air quality and the COVID-19 pandemic. According to the WHO, 99% of the world’s population breathes air that exceeds its guidelines, meaning that nearly every one of us breathes sub-quality air. A recent American study showed that as of 2022, the global air purification market is worth 13.97 billion USD and is expected to grow 7.3% annually from 2023 to 2030, reaching 31.83 billion USD by 20271.
It’s great that people are concerned over the state of the air they are breathing, but this also means that the market is now flooded with air purifiers offering a wide range of technologies, including ultraviolet (UV) sterilisation. UV light has been utilised for decades for disinfection of surfaces, water, and air, but does this technology actually protect us against airborne viruses? Read below to learn more about UV sterilisation technology and how it can protect you from indoor pollutants.
What is UV sterilisation?
UV sterilisation has been utilised for over one hundred years in medical settings. Niels Ryberg Finsen, a scientist from the Faroe Islands, was even awarded the Nobel Prize in 1903 for his work using ultraviolet radiation to combat diseases such as lupus.
Today, you are likely familiar with dermatologists’ warnings about the dangers of the sun’s rays on your skin. The damage to your skin caused by the sun’s rays is due to UV exposure – the outer layers of our skin contain melanin, a pigment that protects us from UV rays. When the outer layers of our skin are exposed to too much UV, it causes them to burn, leaving the deeper layers of skin exposed to cell damage2. UV sterilisation works in a similar way. UV technologies inside an air purifier, for example, target specific bacteria and viruses with the goal of damaging their DNA.
Upon being exposed to UV radiation, the RNA and DNA of microorganisms absorb the rays. More specifically, the radiation cross-links thymine and cytosine (pyrimidine nucleoside bases) within the same DNA strand, and they then become non-pairing bases. This process leads to disturbed abilities to replicate, transcribe, and translate, ultimately causing bacterial cell death and viral inactivation. Simply said, bacteria and viruses can no longer reproduce and are inhibited from growing into colonies that can cause health problems in your body and in the bodies of others when they spread.
One of the great advantages of UV sterilisation is that contrary to other forms of sterilisation (such as antibiotics or hand sanitizers), it does not create bacterial resistance. As a matter of fact, UV sterilisation works against all germs (bacteria, viruses, microbes) regardless of their size or shape. This is why it is a technology that is often found in hospital settings, similarly to HEPA filters.
The different types of UV light
UV light is classified into three different types distinguished by their different wavelengths. The sun produces all three of these types, but each type’s effect on organic matter varies:
- UVA: this is the form of UV light with the longest wavelength (315-400 nanometres). It has the potential to penetrate the middle layer of your skin (the dermis) and is most likely to cause skin damage and cancer.
- UVB: this form of UV light has a wavelength a bit shorter than UVA rays (280-315 nm). Due to their shorter wavelength, they usually do not have the ability to access deeper than the outer layer of your skin (the epidermis).
- UVC: this form of UV light has the shortest wavelength (100-280 nm) and has the highest energy potential of the UV radiation spectrum. Due to their high energy transmission, these rays have the most potential to inactivate microorganisms and pathogens. In the atmosphere, it is blocked by the ozone layer so it does not reach the Earth’s surface. The only way that humans can be exposed to this type of UV light is by artificial means. This is the type of UV light that is used in most air purifiers4.
How does UV light treat microorganisms and pathogens?
There are certain factors that determine how effectively these microorganisms can be inactivated by UV light, the most important of which is the amount of time of exposure. Studies show that 99.99% of airborne pathogens exposed to 40 mJ/cm2 of UV light at a wavelength of 254 nm, the wavelength typically used in air purifiers with UV sterilisation technology, will be inactivated or “killed”3. This level of exposure can take up to several minutes. This is the reason why, contrary to what you might commonly read online, UV technology does not directly sterilise the air. An air purifier’s airflow is far too fast to allow for the required amount of exposure. This is why, to effectively treat the air, it is only fully effective if used in combination with a HEPA filter (or equivalent) that first captures the germs, after which the UV irradiation traps microbes and sterilises the filter.
A systematic review showed that air purifiers containing both UV sterilisation and HEPA-certified filters are the most effective at removing bacteria from the air and reducing the transmission of pathogens5. This is the reason why during the peak of the COVID-19 pandemic, governments in both the UK and in Belgium specifically recommended use of air purifiers containing both HEPA filters and UV sterilisation capabilities.
Is an air purifier containing UV light safe?
It is common for hospital settings, notably operating rooms, to treat surfaces using UVC light with a wavelength of 254 nm (UV light decontaminates within seconds). It has been tested and proven to be an effective way of reducing transmission of pathogens including the MRSA, SARS, and COVID-19 viruses, particularly in rooms that cannot be properly ventilated.
Unlike UVA and UVB rays, UVC rays pose less danger for humans. UVC is a low-penetrating form of ultraviolet radiation, and 4-7% of UVC rays are reflected and absorbed in the first 2 µm of the outermost layer of the skin. This means that the deeper layers of the skin are protected from damage. However, direct exposure of UVC to the eyes can cause temporary damage (symptoms lasting 24-48 hours) and caution must be taken to protect the eyes6.
The UV technology present in Eoleaf air purifiers is located at the centre of the device, protecting the user from any sort of exposure. Our 254 nm UV lamps are also rated as “ozone-free”, meaning that they produce minimal or zero polluting ozone emissions that are harmful for both our health and the environment. Lamps that produce UV light at 254 nm do not create ozone because the energy released is not strong enough to break O2 down into O-. These lamps convert almost all of their energy/heat to UV rays. Note that even "ozone-free" rated UV lamps can emit traces of ozone, which is tolerated in "ozone-free" lamps as long as ozone emissions remain under 0.1 PPM (the level recommended by the World Health Organization). In our lab, we tested our units, and were able to confirm that, if they emit any ozone at all, it would be less than 0.01 PPM. This test was performed simply for the sake of transparency since, even if our units did emit ozone, it would be filtered/reabsorbed by the activated carbon filter and photocatalysis, two other technologies we use in our systems.
This is only several of 8 highly efficient technologies that can be found in our top-of-the-line air purifiers. Refer to our website to read more about our products and the technologies we offer.
1 Advanced Materials. (2018). (publication). Air Purifier Market Size, Share & Trends Analysis Report By Technology (HEPA, Activated Carbon), By Application (Commercial, Residential), By Region (APAC, Europe, MEA, North America), And Segment Forecasts, 2023 - 2030. Retrieved February 26, 2023, from https://www.grandviewresearch.com/industry-analysis/air-purifier-market.
2 U.S. National Library of Medicine. (2022, November 18). Sun's effect on skin. MedlinePlus. Retrieved February 26, 2023, from https://medlineplus.gov/ency/anatomyvideos/000125.htm
3 Beck, S. E., Rodriguez, R. A., Hawkins, M. A., Hargy, T. M., Larason, T. C., & Linden, K. G. (2015). Comparison of UV-induced inactivation and RNA damage in MS2 phage across the germicidal UV spectrum. Applied and Environmental Microbiology, 82(5), 1468–1474. https://doi.org/10.1128/aem.02773-15
4 Center for Devices and Radiological Health. (2023). Ultraviolet (UV) radiation. U.S. Food and Drug Administration. Retrieved February 26, 2023, from https://www.fda.gov/radiation-emitting-products/tanning/ultraviolet-uv-radiation#3
5 MediLexicon International. (2021, October 27). UV air purifiers: Pros, cons, and effectiveness. Medical News Today. Retrieved February 26, 2023, from https://www.medicalnewstoday.com/articles/uv-air-purifier#how-effective-are-they