Mould requires nutrients, water, oxygen and favourable temperatures to grow. Nutrients for mould are present in dead organic material such as wood, paper or fabrics; mould can also derive nutrients from some synthetic products such as paints and adhesives. Mould requires moisture, although some mould species can obtain that moisture from moist air when the relative humidity is above 70 per cent. Many mould thrive at normal indoor temperatures; few if any moulds are able to grow below 4°C or above 37.8°C. Outside this range moulds may remain dormant or inactive; they may begin to grow again when the temperature is more favourable. Temperatures well above 37.8°C will kill mould and mould spores, but the exact temperature required to kill specific species is not well established.

Mould are decomposers of organic material such as wood, plants and animals. Mould and mould spores are found in high concentrations wherever there is dead matter such as a pile of leaves, manure or compost. Mould spores enter buildings through the air or on people, animals and objects that are brought into the building. Spores are small bundles of genetic material and chemicals (similar to seeds) that mould make under certain conditions.

There are only a few mould that can cause infection in healthy humans. Some mould cause infections only in people with compromised immune systems. The biggest health problem from exposure to mould is allergy and asthma in susceptible people. There are more than 100,000 types of mould. Good information has been developed for only a small number of these mould – at least in terms of their effects on human health. Most people tolerate exposure to moderate levels of many different mould without any apparent adverse health effects. Some mould produce powerful chemicals called “mycotoxins” that can produce illness in animals and people. Scientific knowledge about the health effects of these toxins on humans is quite limited.

No. Some individuals have a genetic makeup that puts them at risk for developing allergies to mould. People who have an allergy to mould, especially if they also have asthma, can become ill from exposure to a small amount of mould. Individuals also seem to be quite different in their response to exposure to the toxic chemicals that some mould release. These differences between individuals contribute to the difficult question of determining safe exposure limits for mould.

No one knows the answer to this question for several reasons. Individuals are very different with respect to the amount of mould exposure they can tolerate. Children under the age of one year may be more susceptible to the effects of some mould than older individuals. Measuring or estimating “exposure” levels is very difficult. “Exposure” means the amount of mould (microscopic spores and mould fragments) that gets into a person usually by breathing, but also by eating or absorption through the skin. For example, a building may have a lot of mold in the walls but very little of that mould is getting into the air stream. In that case the people working or living in that building would have little mould exposure.

Although some “experts” claim that individuals have brain damage or have died because of exposure to mould and especially mould toxins, there is no good science at this time to support these claims. Consequently, it is prudent to minimize one’s exposure to really mouldy environments. By “really mouldy” we mean where there are large visible areas of mould (more than a few square feet) or the building has a “musty” odour because of hidden mould growth. There are many epidemiological studies showing that people who live in houses with dampness have many more health problems, especially respiratory, than do people who live in dry houses. This association does not “prove” that it is the mould that is responsible for the increase in illness. However, it does support the assertion that it is not wise to live in damp, mouldy buildings.

Almost all of us already have two effective mould detectors: our eyes and our noses. If black or green discoloration is noticed that is fuzzy in appearance and is in a location that is damp or had been damp, it is almost certainly mould. If a building smells musty, there probably is mould somewhere; the mould may be on boxes stored in a basement or in walls or in the crawl space. If you want to find mould, look for the presence of water or a location where water was likely to have been. If there is still any question about whether the black stuff is mould, have a reliable laboratory examine the material. All you need to know is whether mould is seen when the material is examined under the microscope. An increasing number of companies are offering “air testing for mould.” On the surface, this seems like a reasonable thing to do. The problem, however, is that the results of most air sampling for mould are meaningless for two reasons. Air sampling for mould was not developed to determine if an environment was safe or had a dangerous level of mould in the air. Air sampling was developed to help identify the location of a hidden reservoir of mould. If the source of mould is already identified, air sampling does not provide additional meaningful information. Furthermore, safe or toxic levels of air borne mould have not been established. An individual air sample for mould provides a “snapshot” of what was in the air during the few minutes of sampling. The results may not be indicative of the amount of mould that is in the air during most of the day. Air sampling for mould should be done either to obtain an answer to a question that cannot be answered without the air sampling or to obtain data as part of a research project. The Center for Disease Control (CDC), the U.S. Environmental Protection Agency (EPA) and the American Conference of Governmental Industrial Hygienists do not recommend routine air testing for mould.

The answer depends on how much mould is present and where it is located. If the mould is on furnishings or boxes simply discard the materials. Mouldy materials are not considered hazardous waste; they can be sent to a regular landfill. However, it is smart to seal the mould material in heavy plastic to protect the people who handle it in transit and prevent spreading large amounts of the mould into the building as you carry the material out of it. If the mould is on a hard surface but occupies less than 10 square feet wash the area with soapy water (scrubbing with a brush may be necessary), rinse and allow the area to dry before repainting. If you have asthma, severe allergies and a weaken immune system get someone else to do the clean up. Larger areas (greater than 10 square feet in area) should be cleaned by someone with experience in doing this type of work. Remember, determine what caused the moisture problem and correct that problem. Otherwise, mould is likely to recur.

The answer depends upon what is meant by “completely eliminate mould.” To keep a building completely free of mould spores requires very efficient air filtration and is only accomplished in special situations such as hospital operating rooms and manufacturing “clean rooms.” Remember, mould spores are in the outside air virtually all the time and some of them will get inside buildings. However, it is possible to keep mould from growing inside a building. Moisture control is the key to controlling mould in interior spaces. Air filtration can contribute to lowering mould spores in the air but is secondary to moisture control.

No. Although bleach will kill and decolorize mould, it does not remove mould. Dead mould can still cause allergic reactions. It is not necessary to kill mould to remove mould. Soap and water and scrubbing can remove mould from hard surfaces. The Environmental Protection Agency (EPA), the Center for Disease Control (CDC) and the New York City Health Department agree that bleach or other biocides should not routinely be used to clean up mould.

The mould cleanup is finished when there is no visible mould remaining and there is no dust or dirt remaining that could contain large amounts of mould and mould spores. Routine clearance testing for mould is not necessary. Leaving a few mould spores behind is not a problem if the underlying moisture problem has been corrected. Remember that mould spores are virtually everywhere. Even if all mould and mould spores are removed as part of the cleanup, spores from outside will re-enter that space. The spores won’t be able to grow unless water is also present.