Within the optimum range of 40 to 60% of relative air humidity, aerosols shrink only so far that the salt concentration in the aerosol core increases so much that the germs and microorganisms they contain are killed off.
Excessively dry air also damages the sophisticated protective mechanism of the respiratory tract. The mucous layer dries up, becomes tough and obstructs the movements of the cilia, so that viruses and germs can no longer be removed.
In dry air in particular, germ droplets spread over long distances
and remain contagious for long periods of time. The situation is different with optimal
air humidity between 40 and 60 percent.
In this range, the germ droplets do not travel long distances and they infect fewer people. Thus, optimal ambient air humidity provides effective protection against infection.