Mold Overview and Health Concerns

Molds are microscopic fungi that naturally thrive when moisture is present. In an outdoor environment, molds are beneficial because they help break down decaying matter such as fallen leaves and animal carcasses. Any object, no matter how small, will host molds as long as the following conditions are met:

Without mold, the world wouldn’t be able to enjoy aged cheese and Alexander Fleming wouldn’t have discovered Penicillin, the world’s first antibiotic.

Indoor Molds as a Health Threat

Molds often thrive in indoor environments as well. They reproduce via spores which are invisible to the naked eye. Cladosporium, Penicillium, Aspergillus, and Alternaria are the most common indoor molds. Generally speaking, molds do not pose a health risk in indoor settings unless they are allowed to thrive and multiply in large amounts.

How do indoor molds develop?

Mold spores enter indoor environments through windows, doors, air conditioning systems, heating and ventilation. Spores are transported indoors as they attach to people, pets, clothing, shoes, and other vehicles. Once the spores land on damp or wet materials indoors such as cardboard, tiles, paper, paper products, upholstery and wallpapers, mold growth can be expected.

What health issues are associated with exposure to indoor molds?

In 2004, a report titled “ Damp Indoor Spaces and Health ” was produced by Institute of Medicine (IOM) to better understand the relationships between indoor moisture and public health. The committee responsible for the report found out that people who frequently spend more time in damp corners of the household suffer from symptoms associated with respiratory disorders such as wheezing, coughing, and throat irritation. A segment of the population may even be allergic to molds where the spores themselves can trigger an asthma attack. Health issues resulting from indoor exposure of molds vary from one person to another. The extent of these health issues generally depend on the amount of mold the individual is exposed to, existing allergies, and general state of health.

There are a variety of health issues that can arise from mold exposure which can be classified into the following categories:

In 1986 a report was published in the Atmospheric Environment journal which discussed how an entire household in suburban Chicago experienced chronic health problems due to heavy exposure to Stachybotrys chartarum, a specific type of mold . It turned out that the molds produced trichothecene mycotoxins and the symptoms exhibited by the family members completely disappeared when the mold infestation was substantially reduced.

Symptoms to Look Out For

It has been consistently proven that individuals exposed to mold have one or more of the following symptoms:

Who Are at Risk?

While no one is exempted from the health risks associated with molds, the following groups are at higher risk of developing health issues resulting from indoor mold exposure.

Common Types of Indoor Molds

There are nearly 10,000 species of known indoor molds worldwide. Based on indoor air quality testing, the following species are found to be the most common in indoor settings.

Penicillium - Molds of this species can be found even in clean environments. The toxins produced by Penicillium species has been shown to be carcinogenic in rats.

Aspergillus This type of mold is often found in problem buildings such as antique shops, farms, construction sites, historic buildings, summer cottages and saunas. Aspergillus parasiticus and Aspergillus flavus produce mycotoxins that are known to be the most toxic to vital organs such as the heart, liver, brain, and kidneys. Aspergillus sinusitis is a common condition that could arise from exposure to this type of mold. Symptoms include chronic headache, stuffy nose, and pain in the sinuses. Surgery may be necessary once the fungi has burrowed deep into the skull.

Stachybotrys chartarum - Exposure to this rare indoor mold has been associated with acute idiopathic pulmonary hemorrhage in infants. This serious condition is characterized by severe bleeding in the airways and may or may not be accompanied with respiratory distress.

Molds in the Household

Homes with severe mold infestation typically contain a musty or earthy odor similar to that of a forest floor. Large colonies may be visually obvious and typically take a green, grey, or white color similar to molds commonly found in aged cheese or moldy bread. Often times the mold can appear as tiny black spots as well. On vinyl wall coverings, molds can appear as pinkish to yellowish splotches. When left unchecked, the high levels of moisture can lead to deterioration of gypsum wallboards, resulting in a mushy appearance.

Do I need to test for molds at home?

Currently, the Centers for Disease Control and Prevention (CDC) does not recommend home testing for the type of mold present. If any mold is seen or smelled at home, it is best to have it reduced or eliminated no matter what type of mold is present. Apart from the fact that testing for the type of mold in your home is expensive, there are currently no known standards of normal indoor mold levels.

How do I prevent buildup of molds at home?

It’s more effective to prevent buildup of molds by controlling moisture levels rather than focusing on the removal of organic materials within home. Indoor water spills or leaks should be attended to immediately to prevent or limit mold growth. The same urgency should be applied in water-soaked materials. Additionally, home and buildings should be regularly inspected for signs of water damage.

The following specific actions can be taken to help reduce the formation of mold in the home.

While there are many methods of reducing the buildup and proliferation of mold at home, controlling moisture levels is generally most effective. Individuals who persistently exhibit the aforementioned symptoms without a known cause are encouraged to inspect the home for indoor mold exposure.


The health risks associated with mold growth is the result of the fungi itself or the metabolic products produced by the fungi. Symptoms can be nonspecific but they generally fall in the categories of allergy, infection, nasal mucous membrane irritation, trigeminal nerve issues, and toxicity due to mycotoxins. It’s important to prevent the build-up of moisture to avoid mold growth in the household and create a health environment.


WHO Guidelines for Indoor Air Quality: Dampness and Mould (PDF) - World Health Organization, 2009

2004 Institute of Medicine Report, Damp Indoor Spaces and Health, published by The National Academies Press in Washington, DC

The EPA publication, "A Brief Guide to Mold, Moisture, and Your Home"

The Center for Disease Control and Prevention (CDC's) National Center for Environmental Health (NCEH) Frequent Questions on Mold

Canada Mortgage & Housing Corporation "Fighting Mold - The Homeowner's Guide"

Centers for Disease Control and Prevention: Mold General Information Sheet