Dangers from moulds in living rooms

Health problems caused by moulds

Moulds are a natural part of our environment and therefore also present indoors. However, mould growth in the interior should be avoided. The most common symptoms described in interior mould burdens are non-specific, e.g. conjunctival, throat and nose irritations, cough, headaches or fatigue. Some of these symptoms (conjunctival or nasal irritation) may be associated with both mild allergic and irritant effects. The others are mainly associated with irritant effects.
Epidemiological studies indicate a link between mould exposure and respiratory problems. However, scientifically validated statements on a dose-effect relationship between indoor mold exposure and health complaints of the residents are not possible. Therefore, measured mould fungus concentrations do not directly indicate health effects.

Allergic reactions

Moulds are capable of triggering allergic reactions. One of the possible health reactions of the body to an increased mould fungus concentration in the interior is the occurrence of allergies caused by inhalation of spores. It is assumed that in principle all moulds are capable of triggering allergic reactions in susceptible persons. Often, however, a mould allergy is not detected, as extracts are only available for allergy testing for a few moulds.
The allergic symptoms caused by moulds include rhinitis (symptoms similar to hay fever), asthma and allergic alveolitis. These can develop immediately, within minutes (type I allergy) after spore contact or only after 4 to 8 hours (type III allergy) or 24 to 48 hours (type IV allergy). Rhinitis and asthma attacks occur within a few minutes after contact with moulds and therefore belong to reaction type I.

In people who are already sensitised, even low concentrations of mould, as may occur in low-polluted interiors, can be sufficient to trigger allergic reactions (e.g. asthma attacks).
Exogen allergic alveolitis (EAA = hypersensitivity pneumonia), which occurs much less frequently and almost exclusively in the workplace, is generally triggered by repeated exposure to very high concentrations of spores (106 to 1010 spores/m3), which cannot be expected indoors. In case of permanent exposure the EAA can lead to pulmonary fibrosis. The EAA can lead to the development of specific occupational diseases, such as farm lung. Spores of mouldy agricultural material such as hay, straw, cereals and vegetables play a major role here.

So far, irritant and toxic effects of moulds have been demonstrated – almost exclusively – at contaminated workplaces with high mould fungus concentrations. The importance of these effects in indoor mould growth is unclear. Health problems caused by irritant effects of moulds occur mainly in workplaces where high concentrations of moulds occur.

Organic Dust Toxic Syndrome

Organic Dust Toxic Syndrome (ODTS) is causally associated with the inhalation of very high concentrations of molds (109 spores/m3) or bacteria (1 – 2 µg/m3 endotoxin), as they can occur in production-stressed workplaces but not in the interior.
The clinical picture is characterized by fever, flu-like symptoms and states of exhaustion as well as skin and mucous membrane irritations. The reaction takes place within a few hours after exposure. The clinical pictures described under the terms thresher, cereal and mill fever belong to the ODTS.


Outside the workplace, there are only a few individual descriptions of acute toxic-irritating diseases. However, it remains unclear how low concentrations of moulds and their metabolic products can affect health in the event of prolonged exposure.
It is assumed that toxic substances emitted by moulds, so-called mycotoxins, as well as 1,3-ß-D-glucan and possibly MVOC and other previously unknown metabolic products or components of moulds are involved. In principle, all moulds (and bacteria) are capable of triggering such symptoms. Different types of mould are able to produce mycotoxins.

Unlike in the food sector, data on toxic effects of mycotoxins in respiratory or skin absorption are still very limited at present. However, the results currently available from animal experiments show that mycotoxins that are spread and inhaled via the air can also lead to diseases. Indoor concentrations of mycotoxins are generally low and the effect of such low concentrations on health at long-term exposure is currently unknown. For precautionary reasons, however, the increased occurrence of mycotoxin-producing types of mould in the interior must be critically evaluated.
1,3-ß-D-glucan is a toxin that is part of the cell wall of fungi and can be extracted from fungal hyphae and spores. Like the endotoxins from Gram-negative bacteria, it has an inflammation-promoting effect and was associated with the occurrence of irritation of the mucous membrane and fatigue in investigations in office buildings with poor indoor air quality.


The volatile organic compounds ( MVOC = Microbial Volatile Organic Compounds) produced by moulds, which cause the characteristic mould odour, are called microbial volatile organic compounds.
is a mixture of different substances (e.g. alcohols, terpenes, ketones, esters, aldehydes). Some studies suggest a link between MVOC exposure and health conditions such as mucosal irritation and headaches.
According to current knowledge, toxic effects of MVOCs are not relevant in interiors, as such effects only occur, if at all, at concentrations that are not achieved in interiors.
However, the importance of possible odour harassment caused by MVOCs must be taken into account, as the odour thresholds of some MVOCs are in the lower µg/m3 range.


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