Mould and Yeasts

Mould and yeasts are part of nature and decompose dead organic matter such as dead leaves or animal carcasses. They play an important role in compost, in fermentation processes, for example the production of beer or the fermentation of dairy products into cheese.

Also in buildings, mould can affect furniture or walls and as a result can negatively impact the health of the inhabitants.

Moulds need humidity and a suitable growth medium to live. All organic materials can be used as a growth medium. In a house, wallpaper, wallpaper paste, paints, wood, paper, textiles, plastics and rubber, as well as wall plaster, leather, dust but also potting soil can serve as growth medium and can be degraded.

The most important growth factor for fungi is the humidity of the growth medium. In living areas, humidity production is a direct consequence of the use of the building. In a four-person household, showering, washing, cleaning, cooking, drying clothes but also human sweating produce on average one bathtub full of water per week. Problems with mould occur when the produced humidity cannot escape from the building because too little ventilation is provided.

Other sources of humidity are construction defects such as water pipes leaks, infiltration of rain due cracks in the fa├žade or leaking roofs; thermal bridges due to inadequate thermal insulation; or high residual humidity in new buildings due to building materials such as gypsum, mortar, concrete, screed. Old buildings often have no moisture barrier protecting them from ground humidity, so humidity can rise inside the building walls due to capillary effects.

Moulds primarily release spores into the room air. This is their way of reproduction. The spores fly through the air and if they settle on a suitable moist growth medium, a new mould develops in this location. Various types of mould can also release mycotoxins under certain conditions. These are chemical fungal toxins that are intended to prevent other types of mould or bacteria from growing in these spots. Some of these mycotoxins have been adopted by medicine because they can successfully fight bacteria. We know them not as mycotoxins but by the term antibiotics. Thus, the well-known penicillin is obtained from moulds of the genus Penicillium, the same genus to which Penicillium roquefortii belongs, which is used in the production of blue cheese.

Health Effects of Mould

Moulds can endanger human health in 4 different ways:


Mycoallergoses are allergic reactions to increased spore concentrations in the air. Symptoms of a fungal allergy are inflammation of the eyes and mucous membranes (runny nose) as well as the respiratory tract (cough as well as asthma).

In general, all types of mould can cause allergies. These are mainly type I allergies in which IgE antibodies are formed. Symptoms include itching, conjunctival redness, allergic rhinitis, wheals and shortness of breath (bronchial asthma). These symptoms usually appear within the first half hour after exposure.

Type III allergies to mould (formation of IgG antibodies) and type IV allergies (sensitization of T lymphocytes) are relatively rare. The most commonly flu-like symptoms (fever, cough, shortness of breath, fatigue, allergic alveolitis) usually do not appear until four to eight hours after exposure.

Toxic Effects (mycotoxicosis or mycoses)

Symptoms are varied and affect either the mucous membranes such as the eyes or the skin (physician call it MMI or Mucous Membrane Irritation Syndrome) or the symptoms are flu-like (ODTS syndrome or Organic Toxic Dust Syndrome). The latter is also called “farmers fever”, coming from American farmers that inhale mould spores of spoiled plants.

Mycotoxin Poisoning

Mycotoxins damage the kidneys (nephrotoxic effects), the liver (hepatotoxic effects), the lungs (pneumotoxic effects) or the nervous system (neurotoxic effects). Mycotoxins can also act carcinogenic or reprotoxic, even in very small doses.

Infections Caused by Mould

Infections caused by mould are very rare and mainly affect people with local or general immune deficiencies (HIV-infected, transplanted persons or people after chemotherapy or cortisone therapy). In this case, the moulds settle in the respiratory tract, paranasal sinuses, ear canal or other organs. One example is invasive pulmonary aspergillosis. In healthy people, infections caused by fungal spores are usually avoided by an intact defence mechanism.

What do to in case of mould infestation?

First and foremost a biological examination of the building should be done including mould analyses in order to identify the different mould types and their concentration in the air. It is also important to identify the sources of humidity in order to determine appropriate renovation measures.

Additionally, the medical diagnosis consists of analyses in which the immune response to the detected mould species is identified, either by the presence of certain antibodies (RAST test for IgE antibodies), immune cells (LTT test) in the blood or by a provocation test (e.B. PRICK skin test).

Under no circumstances should moulds be treated with biocides or fungicides, as this would mean to replace a poison by another poison. As alternatives to such “chemical clubs”, a number of proven home remedies, such as high-proof vinegar, high-proof alcohol (70-80%) or a salmiac dilution are available. However, these measures can only temporarily eliminate the mould infestation, since the cause, namely the excessive humidity of the materials, is not eliminated. A permanent solution can ultimately only be obtained by following the decontamination and restauration suggestions recommendations suggested by a building biologist.