In environments with lower than 40% Relative Humidity (RH), droplets from a cough or a sneeze lose their moisture quickly. This results in droplets becoming ‘dry aerosols’ and capable of staying in the air for longer periods. Viral particles remain infectious much longer below 40% and above 80%.
Virus particles are most inactive at 50% humidity, and retain their infectiousness the further from that median value, plateauing at 20% and 80%, respectively2. Staying within 40% to 60% relative humidity is ideal from a comfort perspective but 50% is the most ideal in terms of fast virus inactivation.
Keeping the humidity at the ideal range not only helps you stay comfortable but also keeps you healthy. Low humidity (less than 30%) may promote dry nasal passage which makes people more susceptible to cold viruses while high humidity (more than 70%) may promote mold growth which can be harmful to people with weakened immune systems.