Keeping a healthy humidity level will help combat airborne infections.
The humidity of air is a major factor in the transmission of airborne microbes.
In dry atmospheres below 40%RH expelled droplets rapidly lose their moisture content through evaporation. As smaller droplets remain airborne for longer, this evaporation results in more droplets capable of staying airborne and increases the overall time they can float around.
The droplet’s water loss also changes its structure to a crystallized solid state. Viruses and bacteria get preserved in a floating capsule, where they remain infectious and have a greater potential to infect other people.
In an atmosphere above 40%RH, expelled droplets retain their moisture content, are heavier and less able to remain airborne. Furthermore, the dissolved salts inside the remaining airborne droplets create a hostile environment for any suspended microbes, decreasing their infectious nature and any risk they pose to health.