Plant next to a humidifier that is currently spraying water vapor. Recommendation for indoors is a minimum humidity of 40 percent air humidity
Air quality

Minimum humidity 40 percent: Establish healthy humidity levels

Dry air is a problem especially during the winter heating period: On the one hand, too low room humidity worsens the all-important feeling of comfort. On the other hand, it leads to an increased risk of infection - for example with flu viruses. For this reason, a trade association has launched the Minimum Humidity 40 Percent campaign.


Martin Jendrischik



Humidity generally describes the water vapour content in the air. It is measured as absolute humidity in grams per cubic metre and is defined as the mass of water vapour contained in a specified volume of air.

As a second variable, maximum humidity plays a decisive role: it is defined as the highest possible absolute humidity at a certain temperature. Finally, relative humidity is the percentage ratio between absolute and maximum humidity.

What relative humidity is recommended?

A relative humidity of between 40 and 60 percent is recommended. However, this is often not achieved, especially in public buildings. This is one reason why the German Building Climate Association (Fachverband Gebäude-Klima e.V.). (FGK) has launched the Minimum Humidity 40 Percent campaign. "The aim of the campaign is to raise awareness of the issue among building owners, planners, commercial users and employee representatives," explained Claus Händel, Technical Officer of the FGK at the presentation of the campaign at the Elbphilharmonie in Hamburg.

Air that is too dry deteriorates the skin, affects the eyes and mucous membranes. Our health, our performance, deteriorates. "Especially in public buildings with a high number of visitors, the minimum humidity of 40 percent is elementarily important," emphasised Dr. med. Walter Hugentobler, medical specialist and expert on indoor air humidity.

"The minimum humidity of 40 per cent helps to significantly reduce the risk of infection and increase health well-being."

When is the humidity too high?

In living rooms, the ideal values for relative humidity are 40 to 60 percent - usually at a temperature between 20 and 23 degrees (children's rooms, living and working rooms) or between 17 and 20 degrees Celsius in the bedroom. In the bathroom, the relative humidity may be somewhat higher (50 to 70 percent) - but it is advisable to reduce the humidity by ventilating after showering and to close the bathroom door so that steam does not collect in poorly ventilated areas.

Woman looks into fogged mirror
In the bathroom, the humidity may rise to 50 - 70%.

If the relative humidity is too high - permanently more than 60 percent - the threshold for mould growth is exceeded - provided that the outside walls are significantly colder compared to the room air temperature. Although most types of mould prefer a relative humidity of 80 percent at a temperature of 20 degrees Celsius - some types also develop at lower humidity.

When inhaled, the spores and VOC gases of moulds can cause allergies as well as various other complaints. These include migraine, asthma, cough and cold, conjunctivitis as well as skin changes, joint pain and gastrointestinal complaints.

What influences the humidity in buildings?

The indoor air humidity depends significantly on the usage habits of the house occupants (frequency of showering / cooking), but also on the ventilation behaviour. In winter, unregulated ventilation can exacerbate the problem of low humidity. Environmental influences such as working materials (e.g. paper), furniture or carpets also play a role. In addition, plants, aquariums or indoor fountains have an effect on the air humidity.

In offices, department stores or other public buildings, the problem of too dry indoor air is aggravated by the fact that there is no additional humidity from showering or cooking. Many people with many potential sources of air pollutants make higher air exchange necessary.

However, in winter, conventional ventilation leads to a reduction in room humidity: Because the cold outside air enters a warm room, it warms up from, for example, 0 to 22 degrees Celsius. Consequently, the relative humidity of this heated air cannot exceed 20 percent.

Measure humidity, humidification necessary?

"Humidification should be provided in all areas where a comparatively large amount of fresh air is required. For example, in offices, shopping centres or restaurants," recommend the representatives of the FGK on the website for the Minimum Humidity 40 Percent campaign.

In the living area, the air-Q air analyser or another hygrometer can be used to permanently control the room humidity and establish healthy humidity levels. If it is below 40 percent, humidification is also highly recommended here.

(Cover image: Pexels / Roman Koval; Image 2: Unsplash / Vinicius Amano)

Minimum humidity 40 percent: Establish healthy humidity levels
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