Humidification

Humidification & Airborne Virus Transmission

October 25, 2023·5 min read·TPI Technical Team

In recent years, the world has witnessed the rapid spread of airborne viruses and pathogens, leading to widespread health concerns and significant economic impacts. While measures such as vaccination, social distancing, and mask-wearing have been effective in combating the transmission of these pathogens, a lesser-known yet crucial factor is the role of indoor air quality. This white paper highlights the importance of indoor air humidification as a strategy to mitigate the transmission of airborne viruses and pathogens.

The transmission of airborne viruses and pathogens is a significant concern in public health, particularly during pandemics. Viruses such as influenza, coronavirus, and respiratory syncytial virus (RSV) can spread through respiratory droplets and aerosols. Maintaining proper indoor air quality is crucial in reducing the risk of infection — and one aspect that deserves more attention is humidity levels.

Understanding the Role of Humidity

Humidity refers to the amount of moisture present in the air. The level of humidity in indoor environments can influence the survival, transmission, and infectivity of airborne viruses and pathogens. Numerous studies have shown that maintaining optimal humidity levels can have a positive impact on mitigating the transmission of respiratory viruses.

Impact of Humidity on Virus Survival and Transmission

Virus Inactivation

Studies have demonstrated that higher humidity levels can lead to the inactivation of airborne viruses, reducing their ability to infect individuals. Elevated humidity levels have been shown to disrupt the structure of viral particles, making them less viable and contagious.

Droplet Size and Suspension

Adequate humidity can impact the size and behavior of respiratory droplets. In environments with low humidity, smaller droplets tend to evaporate quickly, leaving behind smaller particles that can remain suspended in the air for longer periods. Higher humidity levels can prevent droplet evaporation, causing larger droplets to settle faster and minimizing the risk of inhalation.

Mucociliary Clearance

Optimal humidity levels support the body's natural defense mechanisms. Adequate humidity assists the mucociliary clearance system in the respiratory tract, which helps expel viruses and pathogens trapped in mucus — reducing the chances of infection.

Scientific Evidence and Expert Opinions

A study published in the journal PLoS ONE found that increasing humidity to 43% or higher significantly reduced the infectivity of the influenza virus. Lower humidity levels (below 23%) resulted in higher viral survival and increased transmission rates.

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends maintaining indoor relative humidity levels between 40% and 60% to reduce the spread of airborne viruses and bacteria.

According to a study published in the journal Pediatric Allergy and Immunology, low indoor humidity levels were associated with an increased risk of respiratory infections in children.

ASHRAE Recommendation

Maintain indoor relative humidity between 40% and 60%

This range is recommended to reduce the spread of airborne viruses and bacteria in occupied indoor spaces.

Conclusion

Indoor air humidification plays a crucial role in mitigating the transmission of airborne viruses and pathogens. Maintaining optimal humidity levels — ideally between 40% and 60% RH — can help inactivate viral particles, reduce the suspension time of respiratory droplets, and support the body's natural respiratory defenses. Proper humidification is a practical, evidence-backed layer of protection for schools, healthcare facilities, offices, and any occupied indoor space.