WASHINGTON (AP) -- Grandma may have been right about keeping a teakettle warming on the stove in winter to moisten the air.
Studies of seasonal influenza have long found indications that flu spreads better in dry air.
Research being published in Proceedings of the National Academy of Science indicates that the key is the absolute humidity which measures the amount of water present in the air, regardless of temperature -- not the more commonly reported relative humidity.
Relative humidity varies depending on air temperature; absolute humidity doesn't.
The correlation with flu and low humidity is important because in cold winter weather, when flu is most common, even a high relative humidity reading may indicate little actual moisture in the air, and the less moisture there is, the happier the flu virus seems to be.
Still, overdoing the moisture can cause other problems, like mold.
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