Main article: Mold health issues

Molds are ubiquitous in nature, and mold spores are a common component of household and workplace dust. However, when mold spores are present in large quantities, they can present a health hazard to humans, potentially causing allergic reactions and respiratory problems.Some molds also produce mycotoxins that can pose serious health risks to humans and animals. Exposure to high levels of mycotoxins can lead to neurological problems and in some cases death. Prolonged exposure, e.g. daily workplace exposure, can be particularly harmful. The term toxic mold refers to molds that produce mycotoxins, such as Stachybotrys chartarum, and not to all molds in general. Causes / Growing conditionsMolds and fungi are found everywhere inside and outside, and can grow on almost any substance when moisture is present.

Molds when they reproduce make spores, which can be carried by air currents. When these spores land on a moist surface that is suitable for life, they begin to grow. Molds are essential to the natural breakdown of organic materials in the environment. Mold is normally found indoors at levels that do not affect most healthy individuals. When these levels become abnormally high as determined by indoor air quality testing or a mold inspection, remediation is recommended to be carried out by a professional remediation company. Because common building materials are capable of sustaining mold growth, and mold spores are ubiquitous, mold growth in an indoor environment is typically related to an indoor water or moisture problem. Mold growth may also be caused by incomplete drying of flooring materials such as concrete.

Leaky roofs, building maintenance problems, or indoor plumbing problems can lead to mold growth inside homes, schools, or office buildings. Another common source of mold growth is flooding.For significant mold growth to occur, there must be a source of water (which could be invisible humidity), a source of food, and a substrate capable of sustaining growth. Common building materials, such as plywood, drywall, furring strips, carpets, and carpet padding are food for molds. In carpet, invisible dust and cellulose are the food sources (see also dust mites). After a single incident of water damage occurs in a building, molds grow inside walls and then become dormant until a subsequent incident of high humidity; this illustrates how mold can appear to be a sudden problem, long after a previous flood or water incident that did not produce a mold-related problem. The right conditions re-activate mold. Studies also show that mycotoxin levels are perceptibly higher in buildings that have once had a water incident (source CMHC).