There have been many unproven theories as to why we tend to catch the flu during winter—more people congregated closer together indoors, less-active immune systems when days are shorter, etc. But scientists recently determined it’s the lower humidity that’s to blame for outbreaks of the virus when it’s colder. That’s because the virus can remain viable longer in the drier air.
What happens is this: A sick person sneezes or coughs, emitting tiny droplets of moisture that carry the virus. In lower humidity, the moisture evaporates quickly leaving the virus lingering in the air. Also, when humidity is low, our nasal passages are drier, which helps the virus stick.
In a simulation, researchers found that an hour after a virus was released in a room at relative humidity of 23 percent or less, up to 77 percent of viral particles retained their infectious capacity. When humidity was increased to about 43 percent, only 14 percent of the virus particles were infectious.