To avoid mold formation, the following selected conditions must be fulfilled:
According to the Deutscher Mieterbund, more than 3.5 million dwellings in Germany have already been affected by mold infections. A result of large-scale field trials with the population. The climate and energy policy of the federal government leads to physically unfavorable building constructions and the inhabitants are forced to save energy. Beneficiaries are the insulation industry and the healthcare industry. The latter can also sell pills to the sick population.
Important reasons for increasing the mold concentration in the dwellings are the reduction of air exchange (dense windows), lower room temperatures, unfavorable building materials or unfavorable wall coatings and small volumes of rooms.
If the apartment is used the same but at a lower room temperature, the relative humidity is increased. This can quickly create molds on the wallpapers. Particularly affected are cold wall surfaces , as for example in the bedroom over the floor at the outer wall. A correct control of the molds takes place only by the elimination of the causes.
Mold is the trivial name for macroscopically recognizable mostly cotton-like mycelia and / or conidia carriers. Fungi that form molds can not be systematically restricted. They belong to different groups. With the mold concept, different structures and phenomena are associated, for example black mold and grimmel, red bread mold, noble mold, pouring can mold, brush mold, head mold and others. In addition, many are referred to as mold, such as, for example, blue mold, gray mold, snow mold and so on  ...
Molds are ubiquitous, that is, these types of fungi are omnipresent. These can, however, lead to a health impairment in humans, if a higher concentration is constantly present in the room air. If mold stresses occur in living quarters, many residents often suffer from eyebrows, headaches or cold symptoms. If the immune system is weakened, it can occur during long periods of inhalation of mold fungus to the allergy . This physical defensive reaction can lead to bronchial asthma and other health problems to the respiratory system. 
The molds are among the microorganisms. Many different groups of micro-organisms, such as bacteria, yeasts, actinomycers, algae, fungi and protozoa, are summarized in this collection. An assignment to the flora or fauna is possible. Algae, bacteria, actinomycetes and fungi are allotted to the realm of plants, especially the microflora; Only the algae are uniquely plants . This is due to the cellulose-like cell wall and the chlorophyll, for example, to generate energy with photosynthesis.
The animal properties of the bacteria, actinomycetes and fungi include, among others, the predominantly chemoheterotrophic lifestyle and the formation of glycogen, a starch-like polysaccharide, also referred to as animal starch. Nevertheless, the cell structure does not permit the assignment to the fauna and an exception is the protozoa, which is clearly part of the animal kingdom. 
In Germany, there are still no mandatory assessment criteria for mold moldings in the interior. The detection of the strain caused by mold fungi serves various purposes, including:
Of the approximately 100,000 molds, about 30 allergens are present. In nature, they have the task of degrading organic matter and making it accessible to the plants as a source of nutrients in the form of soil.  Humans are therefore adapted to the occurrence of mold fungi in their environment and have a high resistance. It does not react very frequently with disease symptoms to a mold fungus exposure.
Small mold limes on the wallpaper on a cool exterior wall surface does not mean that a high mold fungus exposure is present in the room. On the other hand, in the summer, the load of molds in the dwelling is usually high in a sultry air. The mold is nowhere in the room visibly recognizable.
The constitution, the pathogenicity, the total number of the acting fungi and the frequency are decisive for the effect of inhaled mold fungi. The impact on people and their load is essentially the same for outdoor and indoor sources. ( S. 16)
However, it is also necessary to distinguish whether the room is permanently inhabited by the mold fungus or only occasionally entered. For example, a storage room is not inhabited. Optically thin mold layers on surfaces can occur after a major refurbishment or after new construction. The high humidity is caused by the technologically induced setting processes of the building materials. There are short-term phenomena of mold growth. Previously, a sufficiently long drying time was maintained. Depending on the type of construction, the drying time of the binders (cement, lime or gypsum) is approximately 2 years. Through dense windows and also through the under-tensioning track in the attic, the exchange of the humid air is strongly hindered. You can not speak of a defect until it is caused by a bad construction or a false building material. This does not apply to a renovation of the apartment. It helps here only an intensive ventilation and heating.
A mold fungus determination is then useful for the clarification of specific situations,
The actual damage solution can only be done by changing the causes. These are physical and / or specific properties of the building materials and, of course, also the usage behavior.
All fungi are known as mold fungi, which have mainly morphological but also a number of ecological similarities
They are distinguished by the fact that they have a cotton-like, thread-like, thread-like or powdery appearance (moldy) on the surface. This is caused because the growth takes place not only in the material interior, but also on the surface. However, there are also bacteria which show a fungus-like appearance during growth. These include the so-called ray fungi or actinomycetes.
One can stress the characterization of the molds:
Aspergillus and Penicillium are the most common mold fungi (see picture: 2.1.1.). They belong to the Eumycota Division, Class Ascomycetes, the subclass Euascomycetidae, the Eurotiales order, the Eurotiaceae family. They are all saprotrophes, ie fungi that feed on dead, dead or artificially synthesized organic substrates, for example, on foods such as bread, fruits, milk, etc. The fungi develop a very typical genuine mycelium which is richly branched Spreads in the substrate or on its surface.
(Anamorphic fructification), by the formation of endospores (sporangiospores) or exospores (conidia), sometimes chlamydospores. The conidia carriers are each quite typical and offer the most important distinguishing features. Thus in Aspergillus, the conidia-forming hyphae end in a bladder, which is intensively covered with rod-shaped, single-celled organs, and is termed sterm. The conidium carriers of Penicillium branch at the tip into thin branches. Each of these branches carries a sterigma crowned by a conidial chain. The mycelium is more or less colorless. The conidia bear dyes which give the fungus colony its specific color, black, brown, green, yellow or white in Aspergillus and mainly blue-green in Penicillium (also green mold). In Aspergillus the coloring of trace elements is dependent on the found substrate. For example, Aspergillus nieger dyes intensely black (also black mold), if copper is present, else it assumes a light yellow coloring. 
Since the reproduction is effected almost exclusively by the above-mentioned conidia, no conspicuous fruit bodies are produced. If at all sexual reproductive organs are formed, then only tiny ones.
Cell sprouting and formation of shoot cells, such as yeasts or yeast-like fungi, occur only in very rare cases under certain conditions.
Their habitat is preferably the soil, can also conquer other habitats, such as damp rooms or climatic zones. 
The characteristic volatile metabolites of molds MVOC (Microbial Volatile Organic Compounds) include compounds with boiling points of 0-250 ºC and can be assigned to a wide range of different chemical classes, such as the alkanols, alkenols, ketones, terpenen, aldehydes, alkanes, sulfur - containing compounds, ethenes, esters, carbonic acids, etc. Approximately 30 such compounds were detected in indoor rooms and outdoor air until 2001 Of molds can be formed. 
The musty smell is often due to the formation of MVOC by mold fungi or bacteria. The following spectrum of compounds is characteristic:
3-methylfuran, geosmin, 1-octen-3-ol, 3-methyl-1-butanol, 2-pentanol, 2-hexanone, 2-heptanone, 3-octanone and dimethyl disulfide.  In higher concentrations, some MVOCs have a toxic effect. The interior rooms are generally low, which do not contribute to any health impairment. The importance of the MVOC has not yet been sufficiently researched.  It should also be noted that not all volatile metabolites produced by microorganisms are derived from microbial origin. They are also produced by plants, are part of aromas and technical solvents.
Fungi are chlorophyll-free organisms. The fungi feed mainly on heterotrophic organisms living and living organically. 
The essential growth preconditions are closely linked to the presence of water, which is required for the synthesis of cell material and the energy production of the nutrients dissolved in the water. [3a] In our natural environment growth occurs when there is a certain temperature, a sufficiently high relative humidity and the presence of the necessary food substrates over a certain period of time.
If these conditions change, the growth is restricted, if they improve again, even seemingly dead mycelium can germinate again after months. 
Good living conditions are also at a pH of between 2 to 6.5 to 8 and a temperature of 0 ºC to + 40 ºC. Fungus generally favor nutrient media with low pH values, whereas bacteria prefer a neutral to alkaline range. Most organisms grow in a pH range between 6-8 and are called neutrophil. The growth rate of a cell depends on the pH of the surrounding medium. In addition, the metabolism process, the cell morphology, the composition of the cell wall and the cell envelope and the like can also be influenced. [12c] If the pH changes abruptly, usually a change in the pH value of 1 to 2 is sufficient (even for a short period of time), the phase of growth (exponential or stationary phase) can very quickly lead to a death phase will. In the fermentation operation (technical production of microorganisms) this case is called a pH shock. The pH values can also change in the building. This can be mainly caused by the building materials ">lime plaster or silicate boards.
The redox potential of the nutrient solution is also important. Also no demands are placed on the composition of the atmosphere if they are in the usual climatic range.
The nutrient media must be present:
These nutrient media are located in our natural environment and thus also in the building. These include, for example, glucose, maltose and sucrose, Tapet glue, raspberry wallpaper, disperse colors , wood , paper, textiles, plastics and rubber through the added plasticizer, dust, Greases and much more. The respective microorganisms have generally specialized in the degradation of certain substances under certain climatic conditions. Even with approximately the same climatic conditions different fungal concentrations can occur in the rooms.
For a possible increase in the fungus concentration, not only the increase in the room air humidity (denser windows and more economical heating use) or the temperature is responsible. In addition, the presence of certain nutrient media also plays a role. The presence of carbohydrates alone is not enough. There must also be certain trace element cations (for example Co ++, Mg ++) and anions (for example P, S, N). Calcium (limestone CaCO 3) acts as an inhibitor.
The nutrient requirements are still unknown for many microorganisms. Therefore, no pure or defined compounds are used for the cultivation, but complex mixtures such as whey, corn steep liquor or soybean extract are used. These nutrient media are referred to as complex or undefined. [3a]
Today's building and coating materials, as well as, in particular, synthetic household furnishings (due to gasification of solvents or plasticisers), can provide the necessary nutrient substances which are necessary for an optimal growth process or which also inhibit this process. Even the older mortars, for example, those from limescale or Limestone lime are made from a variety of chemical additives to improve the processability. For example, acrylic 2) hydrosol (Depth) to improve the property of the wall surface. What are the interactions? Even if it is to be solvent-free and so the health from today's point of view not endangered. It is precisely these material mixtures that can provide the necessary trace elements and growth factors for the microorganisms. If the households were still almost free of synthetic substances 40 years ago, they have in the meantime turned into small chemical laboratories, starting from fragrances, toilet cleaners, through outgassings from living room textiles and furniture to the building envelope.
The interaction of mold formation and existing pollutants in the room air or chemical trace elements on the surfaces should therefore also be the subject of future research topics and should not be restricted to the ventilation behavior.
The temperature influences the metabolism, the nutrient requirements, the biomass composition of the cell and above all the growth rate of the microorganisms. If the temperature is 10-25 °C below the temperature extremes, the transport processes slow down and the growth rate moves towards zero. On the other hand, a temperature increase in the optimum range causes a disproportionate increase in the growth rate. In practice, this shows why in a building, with approximately the same relative humidity and usage behavior in 5 dwellings, no mold fungus is detected in an apartment. Temperature differences of 2-3 K can be present here. This fact is also taken into account in the following isopleth system.
Image: Isoplethene systems for spore germination of mold fungi (Aspergillus restrictus (left) and Aspergillus versicolor (right). 
Image: Temperature influence on the growth rate of microorganisms
Explanation of the growth curve:
minimum jelly-like membrane, slow transport process
optimal maximum rate of enzymatic reaction
maximum protein denaturation, breakdown of the cytoplasmic membrane, thermal lysis
Microorganisms behave very differently in terms of their demands on optimal temperature conditions. The molds are distinguished according to their optimum growth temperatures, mesophilic molds at 25-35 ºC, thermotolerant molds at 30-40 ºC, and thermophilic molds at 35-55 ºC (max approximately 60 ºC)  The classification with the psychrophilic organisms is to be completed (below 0 ºC to 20 ºC). These mainly include marine bacteria and iron bacteria. Thermophilic bacteria reach their limit at 70 ºC and extremely thermophilic organisms between 80-90 ºC (for example, genera Bacillus and Clostridium), bacteria growing above 90 and 100 ºC are called hyperthermophilic organisms. [12b] The interaction between moisture, temperature and food substance is presented in the isopleth system for spore germination of the mold fungi. [12b] More detailed information in the mold book.
This mold is located in the outer wall of a constantly used room, 1 m below the surface of a hotel complex in Tunisia. The temperature of the room air on March 1, 2016 is 20.4 ºC and a rel. Humidity of 46%. The surface temperature is 18.7 ºC. This would be about 50% relative humidity on the wall surface. The relative humidity during the winter time is mostly below 60%. There are also no major temperature fluctuations. You can clearly see the salt efflorescence on the cement plaster. Salts are strongly hydroscopic. The cement plaster also forms a barrier layer . The moisture from the air is bound by the salt, but it can not escape via a pore structure. There is hardly any ascending humidity here, since very little precipitation falls throughout the year and the ground water level is many meters deep. There is also no downpipe or other water-bearing pipes, which could be broken. On other wall sections on this floor there are no salt deposits and no mold. The cause is therefore the brick wall, the blocking effect of the plaster and the constructive peculiarity exactly at this wall section. The cause in this case is not excessive humidity or poor ventilation.
1) The current energy policy is also to stimulate energy saving, but on the other hand causes a sick population
2) Designation for plastics consisting of polymerized compounds of acrylic acid and / or methacrylic acid. Acrylic acid is the simplest unsaturated carboxylic acid.
 Smith,S.L.; Hill, S. T.: Influence of temperature and water activity on germination and growth of Aspergillus restrictus and Aspergillus versicolor. Transoctions of Brtish Mycological Society Vol. 79 (1982), H. 3, S. 558 - 560
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