In scientific literature, standards and guidelines, different recommendations are given for lower and upper limits of relative humidity for indoor spaces in order to reduce adverse effects on people and their health. However, these limits are not uniform and in some sources only a lower or upper limit is given. Often, scientific publications state an optimal range of relative humidity for humans between 40% and 60%. In this paper, based on the evaluation criteria of comfort, health, and influence on pathogens and pollutants, the results of the considered sources are analyzed and the recommendations are put into an overall context. The results show that the influences of relative humidity should be considered individually for each criterion and that the requirement for a specific target range always represents a compromise. For example, low relative humidities can lead to a higher acceptance of perceived air quality and to a reduction in the proliferation of dust mites and the corresponding adverse health effects. Maintaining moderate relative humidities can significantly reduce eye, skin, and respiratory health impairments and associated absenteeism. With respect to pathogens, depending on the type of virus, relative humidity can affect their inactivation. For example, polioviruses are inactivated to a maximum degree at low relative humidities, influenza viruses at medium relative humidities, and coronaviruses at medium to high relative humidities. High relative humidities reduce the suspension time of particles and aerosols, but should be avoided because of the risk of microbial growth and mold. Overall, therefore, the compromise of a medium range of relative humidity is shown to have the least adverse effects on humans and their health.
Interview on the study with Dr.-Ing. Kai Rewitz
Chair for building and room air conditioning technology,
at the RWTH Aachen
Humid air minimizes the risk of germ droplets
Humidity has a serious effect on the infectivity of germ droplets.
of germ droplets. The risk of infection is minimal at medium humidity levels
and increases sharply with dry room air.
This is shown by the study of Dr. John D. Noti: „High humidity leads to loss of
infectious influenza virus from simulated coughs“ from the year 2013.
At a room humidity of 7 - 23 % RH
the infectivity of introduced germs is 77% after 60 minutes.
At a room humidity of 43 % RH is the infectivity of
of introduced germs after 60 minutes is 15 % minimal.
Influence of air humidity
on people and their health
Technical publication of RWTH Aachen, Chair of Building and
Indoor Climate Technology, E.ON Energy Research Center