Published: Jun 2015 | Journal of Infection (2015) 71, S54eS58

Influenza and humidity – Why a bit more damp may be good for you!

Metz JA, Finn A


Influenza is a major cause of winter-time morbidity and mortality in temperate climates. While the regular “coincidence” of flu epidemics and winter is obvious, the causal relationship is still not well understood. Studies on the role of relative humidity (RH) and temperature on viral survival, transmission and infection rates didn’t demonstrate conclusive trends. A series of exciting recent studies have instead focused on absolute humidity (AH) and demonstrated highly significant correlations with viral survival and transmission rates in both laboratory and epidemiological models.

The paper reviews the evidence for a causal relationship between absolute humidity and 'flu transmission and outlines, how this could lead to a new approach to curbing this and perhaps other viral epidemics in the winter months.


Quote: “There are data to suggest that outdoor AH levels affect humidity levels inside and that simple humidifiers may be adequate to raise AH to levels associated with a significant reduction in influenza virus survival”.

“The prospect of reducing influenza-associated morbidity and mortality by increasing the absolute humidity in nurseries, classrooms, hospitals, homes for the elderly and general public spaces is an exciting and novel potential strategy for disarming 'flu”.

Scientific studies main menu 

Doc's view...

by Walter Hugentobler

Whether absolute air humidity (moisture volume) or relative air humidity (% saturated), outdoors or indoors, is the primary cause that enables seasonal flu epidemics is rather academic. Since we have no influence on outdoor humidity, the practical consequence is in any case the same: we should maintain indoor humidity levels during the winter with hygienic humidification as part of our flu prevention strategy!

Low outdoor absolute humidity is caused by the cold winter temperatures and the air’s reduced ability to hold moisture. A chilly temperature outside means heating systems are turned on inside. When the outdoor air with low absolute humidity enters a building and is heated, the indoor relative humidity plummets.

This creates the perfect indoor climate for flu virus survival and transmission between occupants. It also increases the susceptibility of occupants by weakening the mucociliary barrier function of the human respiratory system - that's why a bit more damp may be good for us!

Other scientific studies relating to humidity and airborne infection