Low air humidity affects both health and well being of people. During the wintertime, the air inside buildings is heated to a temperature of 20-25°C with the consequence that relative humidity decreases to values of 10-30%, which is perceived as dry air, even if there is fog outside. The dry air favours the evaporation of water from the skin, which cracks and causes dryness of the throat and nose and the respiratory tract etc.

favouring the onset of typical winter illnesses. It is for this reason that air-conditioning systems that control both temperature and humidity of the air are used in hospital wards; the latter being maintained not too low but also not too high