Dry air and the transmission of viruses

Dry air and the transmission of viruses

Certain respiratory infections tend to be more common during the wintertime. “Book of Epidemics”, written by Hippocrates in Greece around 400 BC, includes one of the earliest statements regarding the winter-related outbursts of respiratory infections. According to studies, most respiratory viruses show seasonal trends in the rates of infections. Different types of viruses tend to reach infection peaks at different times of the year. Coronaviruses, including SARS-CoV-2 (COVID-19), show a tendency to reach peak infections during the winter months. A warm and wet climate seems to be related to a reduction in the spread of COVID-19. What are the reasons for higher infection rates of COVID-19 and other viruses during winter? 

Most of our activities during, especially during winter months, happens in enclosed spaces – we work, socialise, commute, or spend most of our time indoors, where we share the air with other people. Because the temperature outside is cold, we are seeking comfort in heated buildings and vehicles. Currently, our indoor areas rely mostly on convectional heating systems to deliver warmth. Infrared heating systems, despite offering significant improvement in terms of air quality and growing in popularity in other European countries (especially Scandinavian countries), are still not common in the UK.

The key feature of convectional heating systems is that they use air as a medium for heat delivery. Radiators heat the air, which travels to the top areas of the room and begins to circulate in an exchange with the cold air cumulating at the bottom parts of the space. This method of delivering heat is not only inefficient but also creates lots of air and dust movement as well as lowers our indoor air humidity. Optimum indoor air humidity is between 40-60%, while the humidity level of the indoor air with conventional heating systems working to provide a refuge from cold winter temperatures falls below that safe level.

According to many studies, dry air is the main factor that improve the transmission of viruses, including COVID-19. Respiratory virus infection can happen through contact with infected people or contaminated surfaces; through larger viral droplets exhaled by infected people that travel for short distances and fall on the surfaces; or through aerosol long distances transmission, where small viral droplets exhaled by infected people that, due to their smaller size, evaporate quickly and remain in the air for a longer time before they can eventually drop to the surfaces. 

Hot and dry indoor air causes more rapid viral droplets evaporation and their shrinking. This helps the droplets remain in the air for a longer time and travel for longer distances (more than 2m). Together with poor ventilation, this creates a perfect environment for the spread of viruses.

Moreover, dry air, not only facilitates viral transmission but also impairs our immune response. It causes our airways to lose their moisture. The air we breathe contains dust, pollens, bacteria, and viruses. That is why our respiratory tract is equipped with a mechanism that removes these foreign bodies and prevents them from entering further into our respiratory system. Our respiratory tracts are lined with hair-like cells called cilia, and Goblet cells. Goblet cells create a level of mucus that traps the foreign bodies. Cilia produce wave-like coordinated movement that moves the mucus with trapped pathogens and removes them from our airways via coughing or sneezing. Low humidity indoor air dries up the mucus. This impairs catching the pathogens and immobilizes cilia. The pathogens, including viruses, cannot be expelled from the airways in the early stages effectively and can easily enter further into our respiratory system. That is one of the reasons why our immune responses are less efficient in a dry air environment.

Considering the results of the studies on the role of indoor air humidity in the transmission of the viruses introducing public building regulations regarding air humidity would be beneficial: “Based on research findings, for future scenarios, setting a minimum RH (relative humidity) standard of 40% for public buildings will not only reduce the impact of COVID-19, but it will also reduce the impact of further viral outbreaks, both seasonal and novel” (An Overview on the Role of Relative Humidity in Airborne Transmission of SARS-CoV-2 in Indoor Environments – Aerosol and Air Quality Research ( ). 

All things considered our product iHelios has a potential to offer a healthier alternative to convection heating systems. iHelios system uses infrared radiation and delivers heat in a completely different way to convection heating systems. Instead of heating the indoor air, infrared waves directly warm the objects, such as walls, furniture, and people. Because infrared rays do not heat the air, the air humidity does not drop radically, like with standard heating systems. It seems like a logical conclusion to draw that iHelios system can create a healthier environment in comparison to traditional heating systems do. Additionally, iHelios does not rely on air circulation for heat distribution, which creates less air movement in the indoor area and reduces the spreading of the dust and viruses contained in the air. Reduced air movement combined with an open window sensor allows proper circulation without a worry about great heat loss.

iHelios vs. Radiators


Seasonality of Respiratory Viral Infections | Annual Review of Virology (

An Overview on the Role of Relative Humidity in Airborne Transmission of SARS-CoV-2 in Indoor Environments – Aerosol and Air Quality Research (

How humidity may affect COVID-19 outcome (

Coronavirus SARS-CoV-2 spreads more indoors at low humidity: Indian-German research team recommends at least 40 percent humidity in public buildings — ScienceDaily

Coronavirus disease (COVID-19): How is it transmitted? (

What Causes High Humidity In A House? – Fresh Air Guru

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