What are the problems caused by mold

Sick from mold in the house

Environmental medicineby Angela Haese, Berlin

Headache, tiredness and cough - the cause of the discomfort could be hidden under the wallpaper or in the damp bathroom: mold. In addition to general symptoms, the fungi sometimes also cause allergies or even systemic mycoses.

Indoor mold is a major problem in Germany. A study by the University of Jena of 5000 apartments showed that mold and moisture problems exist in every fifth room. However, the mushrooms not only damage aesthetics, but can also affect health. The Federal Association for Environmental Consulting recently organized an interdisciplinary conference on this topic in Berlin.

Molds grow practically anywhere in moisture and warmth. An ideal prerequisite for their growth is moisture, which appears in liquid form on surfaces after falling below the dew point temperature. Buildings with moisture damage or incorrectly implemented thermal insulation therefore offer ideal growth conditions. The formation of mold can only rarely be traced back to poor hygiene or insufficient ventilation, but is usually a problem in terms of building physics.

Once the fungus has established itself, it spreads its spores. Since these float in the air with an average diameter of around 10 µm, people ingest them through the airways. Numerous epidemiological studies in recent years have shown that health problems occur much more frequently in apartments with moisture damage and mold infestation than in damage-free apartments, said private lecturer Dr. Caroline Herr from the Institute for Hygiene and Environmental Medicine at the University of Giessen and member of the Indoor Air Hygiene Commission of the Federal Environment Agency at the conference. The most common occurrences are irritation of the respiratory tract and allergies.

The experts assume that basically all mold spores can trigger allergic reactions in sensitive people after inhalation. These include symptoms similar to hay fever, asthma and, with extremely high spore concentrations in the range of 106 to 1010 spores / m3, which only occur in special workplaces, exogenous allergic alveolitis (inflammation of the alveoli). In Germany, around 5 percent of the population are sensitive to mold. The risk of developing an allergy depends on the individual predisposition, the allergen concentration and the allergenic potential of the spores.

According to some studies, people in indoor areas exposed to mold can also cause irritation of the mucous membranes and conjunctivitis, which are summarized under the umbrella term "Mucous Membrane Irritation Syndrome" (MMI). Mold infections are rare, but can be life-threatening. Immune-weakened people, such as people after transplants, HIV-infected people or cancer patients after chemotherapy, are considered at risk.

"There is a lot of evidence from various sources that there is an increased risk of respiratory problems from mold exposure," said Mr. However, there is still no known mechanism that could explain the connection between indoor mold infestation and health problems.

Different components of the organisms come into question as the cause of the harmful effects of mold spores. These include mycotoxins, the toxic effects of which in some cases have been well documented in food. The aflatoxin of the species Aspergillus flavus is fatal even in the milligram range. However, there is currently no information on the health risks associated with long-term exposure to mold spores caused by mycotoxins. The spores of Stachybotrys chartarum are an exception. They can contain toxins from the trichothecenes group, which can be absorbed through skin contact or inhalation and which can be harmful to health. They cause a wide variety of symptoms such as headache, dizziness, skin irritation, a feeling of flu or nosebleeds.

In addition to mycotoxins, components of the cell wall of fungi, such as 1,3-β-glucan, which has a pro-inflammatory effect, can also impair health. This compound has been linked to irritation of the mucous membranes and fatigue in poor air quality in office buildings. According to some studies, the volatile organic compounds (MVOC, microbial volatile organic compounds) synthesized by molds could also be the cause of health problems such as irritation of the mucous membrane and headaches. MVOC are mixtures of terpenes, ketones, esters and alcohols that are responsible for the typical mold odor. According to the current state of knowledge, however, they occur in concentrations that are non-toxic.

“Research into the effects of the various substances in mold on the human body is not enough. Therefore, no information can yet be given about a threshold value up to which no adverse health effects are to be expected, ”said Nicole Richardson, expert for mold and indoor pollutants at the IHK Witten. That is why environmental medicine specialists like Herr demand: "From a preventive point of view, one should intervene to minimize mold exposure."

No uniform guideline values

Various problems can arise when analyzing and assessing mold infestation indoors. Moisture damage and fungal attack are not always easy to recognize. The determination of the spore germ count in the air, the detection of mold-specific MVOC or the determination of the germ count of mold spores in house dust provide information on mold sources. From the point of view of mycologists, the study of the germ count in the air is of central importance, since the microorganisms present in the air are recorded directly. For this purpose, special particle collectors collect the fungal spores from a defined volume of air and place them on special nutrient media for cultivation. A comparison of the colony-forming units (CFU / m3) of indoor and outdoor air shows whether there is a source of mold in the indoor area. The problem then lies in assessing when there is normal exposure and when it is necessary to remediate, said Richardson. Indoor concentrations of over 2000 CFU / m3 are now considered to be a serious health risk. The decisive factor for this assessment is a study in which, with a mold concentration of more than 2400 CFU / m3 indoor air, health complaints such as coughs, headaches and rhinitis were found in all residents of the building examined. Generally valid values, limit values ​​or standardized guide values ​​for Germany do not yet exist. According to new studies, more than 110 CFU / m3 Aspergillus and Penicillium spores indicated an indoor source, but did not necessarily represent a health problem, according to Herr.

In order to assess an infestation and draw up a remediation concept, experts therefore also use the composition of the mold species in the interior. Hundreds of different species can occur here. Eleven of them, including Stachybotrys chartarum, serve as indicators of moisture damage. The experts usually determine the species based on the morphology under the microscope. Once the fungus species, spore concentration and source have been determined, examinations of the material samples provide a further basis for the experts to decide whether and which remedial measures should be taken. Anyone who fears health impairments from indoor mold can seek advice from health authorities and consumer advice centers. The Federal Environment Agency offers a brochure on the subject of mold pollution in the house at www.umweltbundesamt.de/uba-info-medien/index.htm.


Mold science Molds are a systematically heterogeneous group of fungi that form a macroscopically recognizable mycelial lawn and, with few exceptions, have harmful effects on humans. In total, the group includes 200,000 different species. Well-known types of mold are Aspergillus (watering can mold), Rhizopus (common bread mold), Penicillium (brush mold) and Mucor (head mold).

The heterotrophic organisms feed on organic material such as rotting fruit, bread, nuts, wood or earth. The mycelium, which consists of many branched fungal threads (hyphae), forms first on the surface. This filamentous structure then creates a large number of protruding special hyphae on which the spores or conidia of the mostly asexually multiplying fungi sit.


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