Nadine Walder , 18 June 2024

Dehumidify the air

Avoid mould growth: Formation and causes of mould

Mould in the house or flat is not only unsightly, but can also cause serious health problems. To prevent mould growth, it is important to know the causes of mould and take the right preventive measures. In this blog post, you will find out how mould develops, which factors promote its formation and, above all, how you can effectively prevent mould in your house or flat.


Estimated reading time: 6 minutes


Read on to find out: 

  1. What is mould?
  2. Causes and development of mould
  3. Preventing mould growth: how it works 
  4. Recognising and eliminating the cause of mould  
  5. Mould in rented flats  

What is mould?

Mould is a collective term for various types of fungi that grow on organic materials and spread through microscopically small spores. These types of fungi belong to the group of microorganisms and are widespread in nature. Mould fungi are able to survive even under extreme conditions and grow particularly well in damp and warm environments. 

In nature, moulds play an important role in the decomposition of organic material. In doing so, they make nutrients available for other living organisms. It is estimated that there are around 250’000 different types of mould, of which 100’000 are known. Not all of these moulds pose a danger to humans. Some moulds are used, for example, in the production of medicines or to refine cheese. However, moulds can cause considerable problems indoors and affect our health. 

These types of mould are found in flats and houses and can pose a risk to our health: 

  • Black mould: This species is particularly common indoors in corners, behind furniture or on wallpaper. It requires a humid environment for optimal growth. Black mould is often found in the bathroom near windows or in other places with high humidity. Allergy sufferers and people with a weak immune system can fall ill from the spores of the fungus. Symptoms include allergic reactions, respiratory problems and reddened eyes. Black mould is also suspected of being carcinogenic. 
  • Green mould: This type of mould spreads on various foods and poses a health risk due to the release of mould toxins. It also finds ideal growth conditions on damp ceilings and walls, especially in poorly ventilated areas such as kitchens and bathrooms. The spores of green mould can cause severe allergic reactions, which can lead to irritation of the mucous membranes, fatigue, migraines and respiratory illnesses. 
  • Red mould: Red mould mainly affects cereals and cereal-based products. This type of mould is therefore often found in bakeries. This mould is often a reason why bakers suffer from respiratory diseases. Red mould thrives on foods with a high sugar, starch and carbohydrate content. Paper and wood are also frequently affected, as cellulose is one of the preferred nutrients of red mould. 
  • White mould: This often occurs in corners of ceilings and floors, behind large pieces of furniture, on cold exterior walls and in damp, cool rooms. It can be recognised by a musty smell and the increased presence of vermin such as cellar rattles and silverfish. White mould is also harmful to health: it can irritate the mucous membranes, leading to colds, skin problems, sinusitis and bronchitis. 
  • Yellow mould: This is one of the most dangerous types of mould, but rarely occurs in living spaces with good hygiene standards. Yellow mould mainly grows on cotton fabrics and upholstered furniture. It appears as a brownish-yellow coating with a greasy or dry surface. Yellow mould is harmful because it contains the toxin aflatoxin, which is associated with heart failure and liver cancer, among other things.

Causes and development of mould

Moisture is the main cause of mould growth. It can be caused by condensation, water damage or excessive humidity. If the relative humidity is above 60 % for a longer period of time, the risk of mould growth increases. Condensation often occurs on cold surfaces such as windows or walls. Water damage caused by burst pipes, leaking roofs or flooding also provide ideal conditions for mould growth. 

Structural defects such as poor insulation and thermal bridges (also known colloquially as cold bridges) can contribute to mould growth. Insufficient insulation leads to temperature differences, which can cause moisture to condense and mould to form. 

Living habits also play a role in mould formation. Mould can form, for example, if large pieces of furniture are placed too close to cold exterior walls or if there is insufficient ventilation. Too low a room temperature and inefficient heating also favour the growth of mould.

Avoid mould growth: How it works

  • Ventilate properly: Regular air exchange is crucial to reduce humidity. Shock ventilation is more effective than leaving the windows permanently ajar, as it transports the air out more quickly and does not cause the walls to cool down too much. By airing your home two to four times a day for a few minutes, you are already ensuring good air circulation. 
  • Sufficient heating: A room temperature that is too low promotes the growth of mould. You can find out all about the connection between heating and mould growth in our blog post "How economical heating can lead to the formation of mould". As a rule of thumb, the room temperature should not be below 19 °C. 
  • Reduce sources of moisture: Reduce sources of moisture in your home. Eliminate water damage immediately and use a hygrometer to check the humidity. 
  • Adapt your living habits: To prevent mould growth, you can also adjust some of your living habits. Always air the room immediately after showering or switch on the ventilation to remove moisture to the outside. Always use the extractor bonnet when cooking, if available. Do not dry your laundry indoors or follow the corresponding instructions for drying laundry indoors
  • Use a dehumidifier:dehumidifier reduces the moisture in the air and thus ensures an ideal relative humidity. All Stadler Form dehumidifiers are equipped with a hygrostat that switches the appliance off automatically as soon as the desired humidity level is reached. If the humidity rises above the set value again, the dehumidifier switches on again automatically so that your home never becomes too humid. 

However, these tips do not necessarily guarantee the prevention of mould growth. In many cases, the construction method is to blame for the formation of mould or there are already mould spores in the walls. In this case, these tips will do nothing. If mould is already present, a specialist should always be consulted.

Recognising and eliminating the cause of mould

Mould detection 
Early detection of mould is crucial in order to avoid major damage and health risks. Regular inspections of the home are helpful. Look out for the following signs: 
  • Discolouration: Black, green, yellowish or white stains on walls, ceilings or furniture. 
  • Musty smell: An unpleasant, earthy odour can indicate mould. 
  • Damp spots: Look out for condensation on windows or damp patches on walls. 
To monitor the humidity, you should place a hygrometer in every room. These devices measure the relative humidity and help you to recognise critical values in good time.

Mould removal 

Mould removal is a demanding task that should always be carried out professionally and in compliance with protective measures in order to avoid the spread of spores and health risks. In the event of mould infestation with an area larger than a credit card, for example, a specialist should always be called in. Experts can determine the exact cause of the mould and take appropriate measures to remove it.

Mould in rented flats

If you live in a rented flat and discover mould, it is important to report this to your landlord or landlady immediately. Landlords are obliged to remove mould and remedy the causes. They also have the burden of proof as to whether the mould was caused by misconduct on the part of the tenant. If the landlord or landlady does nothing about the mould in your rented flat, you should consider taking legal action or, in the worst case, moving out to protect your health. 

To summarise, it can be said that regular checks and preventive measures are crucial. Unless there are problems with the construction, the most effective measures to prevent mould growth are proper ventilation and heating, reducing sources of moisture, adapting living habits and using a dehumidifier.


Would you like to find out more about how a dehumidifier can help you feel better or what different dehumidifier systems are available? You can find more information on our information page about humidifying the air.

More about dehumidifying the air


If you have questions related to indoor room climate, please get in touch with us. Or subscribe to our newsletter to regularly get informed about current topics regarding indoor climate, experience reports or Stadler Form insights. 

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