Humidity is an important parameter for health and comfort. Above all, relative humidity is the significant factor - it indicates the extent to which air is saturated with water vapour.
With relative humidity of 50%, the air contains just half the maximum amount of water vapour that it could at the right temperature. At 100% relative humidity, the air is completely saturated with water vapour. If 100% saturation is exceeded, the excess moisture condenses into condensate.
Therefore, relative humidity can indicate how fast evaporation will take place or the likelihood of condensation forming. As the evaporation of moisture through skin is determined by the relative humidity of the ambient air, the latter is an important parameter for the feeling of comfort.
Therefore, health authorities recommend relative humidity of around 50% for living spaces and offices. However, in closed, well ventilated and well heated rooms this value is often not attained, which may have an adverse effect on breathing, skin and mucous membranes. This is particularly the case in winter, as the cold outside air only has a low absolute humidity; when this is warmed up to room temperature, the relative humidity drops dramatically. On the other hand, excessive humidity prevents proper regulation of the body temperature through sweating, and is therefore quickly experienced as being humid.