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A new petition by leading members of the global scientific and medical community calls on the World Health Organization (WHO) to take swift and decisive action to establish global guidance on indoor air quality (IAQ), with a clear recommendation on the minimum lower limit of air humidity in public buildings. This move would reduce the spread of airborne bacteria and viruses in buildings and protect public health.
The petition is designed to not only increase global awareness among the public on the crucial role IAQ plays in physical health, but also to call emphatically on the WHO to drive meaningful policy change.
As COVID-19 continues to put pressure on health systems and the economy globally, the group calls on WHO to review the extensive research that shows an indoor humidity level between the 40 to 60 percent relative humidity (RH), is the optimum threshold for inhibiting the spread of respiratory viruses such as influenza. This is a threshold that many public buildings drop below every winter.
Evidence shows the important role indoor humidity levels play in preventing virus transmission and improving immune system response. There are three key notable findings suggesting why indoor air should be maintained at 40 to 60 percent RH in public buildings such as hospitals, care homes, schools, and offices throughout the year:
Breathing dry air impairs our respiratory immune system’s ability to efficiently capture, remove and fight airborne viruses and germs, rendering us more vulnerable to respiratory infections.
- when the RH is lower than 40 percent, airborne droplets containing viruses, such as SARS-CoV-2, shrink through evaporation making them lighter which enables the particles to float for longer in the air, increasing the likelihood of infection; and
- the vast majority of respiratory viruses suspended in dry atmospheres survive and remain infectious for much longer than those floating in air with an optimum humidity of 40 to 60 percent RH.
The petition specifically and directly targets WHO, due to the pivotal role the organization plays in setting global guidelines for IAQ. Currently, there are no recommendations from WHO on the minimum lower limit of humidity in public buildings. If WHO publishes a guidance on minimum lower limits of humidity, building standards regulators around the world would be encouraged to act urgently.
This petition would do well to add the related issue of ventilation and filtration. Increased air changes, whether through a ventilation system or simply by opening windows and doors, or careful use of fans, can significantly reduce reduces indoor air viral load.