Mold and its health effects

What is mold?

Strictly speaking, "mold" (or "mould" in British spelling) is more of a colloquial name rather than a proper scientific term. This name applies to fungi that have a specific "moldy" look. Fungi, in turn, are one of the major divisions of living organisms (kingdoms), along with animals, plants, protists and two groups of bacteria.

The fungal kingdom includes mushrooms, yeasts, plant pathogens, molds and numerous other groups that are less known to the general public. None of these categories is confined to a single taxonomic group with a common evolutionary ancestor.

Fungi typically referred to as mold are the ones able to grow relatively fast on food and building materials and that have a furry or velvety appearance. "Mildew" is another colloquial name commonly used alongside "mold." It means about the same thing but is often used for fungal growth that looks powdery or slimy.

What mold needs to grow

In order to grow, molds require food, water and appropriate temperature. Different mold species have different food preferences, but overall they are not picky and can use a wide range of organic chemicals. Cellulose, one of the major components of drywall and wood, can serve as the sole source of nutrition for most of them. Plasters often contain organic additives that also make them susceptible to mold growth.

Normal indoor temperatures are perfect for mold growth, so those two conditions are usually met. Water is the key factor. Moisture levels in building materials inside human dwellings should not be high enough for mold growth, but they do reach that level sometimes for many different reasons.

These reasons can be straightforward and easy to fix, such as pipe and roof leaks, or quite intricate, such as improper design of the HVAC system. In bathrooms and basements, excessive moisture can be very difficult to manage, and in those cases the solution may be to eliminate the food source instead.

Mold and health

Many common indoor molds are known to be opportunistic pathogens. That means they do not infect healthy individuals but can infect people with weakened immune systems, such as AIDS patients and people with organ transplants who must take immunosuppressants to prevent rejection.

More often, the harmful effects of indoor molds are caused by their production of allergens or toxins. Potential allergens are produced by a broad variety of indoor molds, but susceptibility to them varies greatly from person to person. Allergic responses include hay fever type symptoms such as sneezing, runny nose, red eyes and skin rash.

Toxins in doses high enough to cause health effects are produced by a smaller number of indoor mold species. The most important toxic molds are two species commonly occurring in conditions of consistently high moisture: Stachybotrys chartarum and Chaetomium globosum.

Many symptoms and human health effects have been attributed to inhalation of fungal toxins (mycotoxins), including: irritation of mucous membranes, skin rash, nausea, immune system suppression, acute or chronic liver damage, acute or chronic central nervous system damage, endocrine effects and cancer. Mold products can also cause or contribute to asthma, acting either as allergens or as non-allergenic irritants.

Odor and MVOCs

Microbial volatile organic compounds (MVOCs) are another group of chemicals produced by fungi as well as other microorganisms. Unlike toxins and allergens that are attached to mold particles, MVOC molecules are light enough to pass through completely sealed but porous building structures.

MVOCs are responsible for the moldy or earthy smell associated with mold. At this time there is no strong scientific evidence about their direct health implications, but the smell is often an important clue when investigating indoor mold growth.