How does mold affect health?

Apr 17, 2020

In previous blog posts, we highlighted the positive ways mold has benefited society.  It is not a secret, however, that mold can also have a negative impact on human health, which this blog will discuss. Please keep in mind that we are not healthcare professionals, and any information posted in this blog is based on literature research. Please follow your doctor’s recommendations and advice. 

Upper Respiratory Tract Health Effects Vs. Lower Respiratory Tract Health Effects

When studying the health effects of mold, researchers identified two ways that mold affects human health. One way is by impacting the upper respiratory tract (URT), which includes the nose, mouth, sinuses, and throat. The other area affected is the lower respiratory tract (LRT) which includes the windpipe (trachea) and the lungs Institute of Medicine. 2004. Damp Indoor Spaces and Health. Washington, DC: The National Academies Press. . 

Symptoms that affect the URT are nasal congestions, sneezing, runny nose, and throat irritation Institute of Medicine. 2004. Damp Indoor Spaces and Health. Washington, DC: The National Academies Press. . Symptoms that impact the LRT are coughing, wheezing, and shortness of breath Institute of Medicine. 2004. Damp Indoor Spaces and Health. Washington, DC: The National Academies Press. .  Research published in “Damp Indoor Spaces and Health” found that there is enough evidence to suggest that there is an association between “the presence of ‘mold’ in a damp indoor environment and upper respiratory tract symptoms” Institute of Medicine. 2004. Damp Indoor Spaces and Health. Washington, DC: The National Academies Press. . In terms of LRT symptoms, there is enough evidence to suggest an association between a damp, moldy indoor environment having wheezing or coughing symptoms Institute of Medicine. 2004. Damp Indoor Spaces and Health. Washington, DC: The National Academies Press. . However, studies did not show enough evidence to support an association between the presence of mold in a damp environment and shortness of breath Institute of Medicine. 2004. Damp Indoor Spaces and Health. Washington, DC: The National Academies Press. . 


Some people may be allergic to certain foods such as wheat or peanuts, or animals such as cats and dogs. Mold also contains allergens that can affect a hypersensitive person. Hypersensitivities to mold may cause allergic rhinitis, allergic conjunctivitis, and allergic asthma.  Allergies are specific to an individual, which means the majority of the population may not be affected. Some researchers believe that 20% of the population is affected by mold allergies Downs, S.H., Marks, G.B., Sporik, R., Belosouva, E.G., Car, N.G., Peat, J.K. Continued increase in the prevalence of asthma and atopy, Arch Dis Child 2001, 84, 20–23. . Allergic reactions to mold occur when the body’s immune system has an overreaction to mold spores. Symptoms may include a runny nose, itchy eyes, wheezing, difficulty breathing, and flu-like symptoms. It is important to note that an individual may be allergic to one type of mold but not another. People aren’t allergic to mold in general– they are allergic to specific types based on unique proteins found on their spores.

Fungal Infections In the Body

We have posted several blog posts indicating where mold can grow in the home, the common causes of mold, and inspecting a home for mold. We have not covered how mold can grow in the human body.

In order to grow, mold has a few demands. It needs moisture and a nutrient source. Both requirements can easily be found in the human body. We are made of organic material, which serves as a perfect nutrient source, and we are roughly around 60% moisture by weight. Fortunately, the human body is equipped with an immune system that attacks foreign invaders. Those that have immunocompromised systems are not so fortunate. An immunocompromised individual has a weakened immune system.  These individuals have a much tougher time fighting infection. When a person succumbs to a fungal infection, it is called mycosis. 

Aspergillus fumigatus is a species of mold that can cause a health condition called Aspergillosis in people with weakened immune systems. Most people breathe in this type of mold all the time and are fine. Folks with weakened immune systems may become sick from breathing it in. It can cause “inflammation in the lungs and allergy symptoms such as coughing and wheezing” . There are different types of aspergillosis diseases that can enter the body through a break in the skin. Cutaneous aspergillosis, for example, may occur after surgery. Most molds find the human body temperature of 98.6°F (37°C) to be too hot; but not Aspergillus fumigatus, which explains why it is the most common cause of various mycoses. 

Histoplasmosis is another fungal infection that can cause fever, cough, and fatigue. Histoplasmosis is caused by a fungus called Histoplasma which can come from the “soil that contains large amounts of bird or bat droppings” . Histoplasma can mainly be found in the soil in the central and eastern states of the United States. When the soil is disturbed the spores from the soil are kicked up into the air. People breathe in the mold spores and most individuals will not get sick. Those that do get ill usually recover on their own without needing medication. Those with weakened immune systems have the potential to get sick.  The infection becomes more serious when it spreads from the lungs to other organs in the body . Another well-known fungal infection is Valley Fever caused by Coccidioides.

All of these fungal infections are caused by viable mold. The best way to understand viable vs. non-viable mold spores is to think of a seed. A non-viable mold spore is like a seed that is in an environment without water — it is dormant. While a viable spore is most similar to seed that is an optimal environment for growth — it will likely grow.

Mycotoxins and Health

As some molds grow, they can produce mycotoxins. Not all mold species have the ability to produce mycotoxins.  Those that generate mycotoxins only make them when necessary, for example when there is competition or limited resources. Mycotoxins are non-volatile so they are not a gas but a physical substance found on mold itself. So for a mycotoxin to be airborne, the surface on which it is found, such as a mold spore, must become airborne, which can happen when it is disturbed. Viable and non-viable spores can have mycotoxins present. 

Microbial volatile organic compounds (mVOCs) are different from mycotoxins. These are produced from actively growing mold, which generates mVOCs when the organism is metabolizing nutrients. A musty odor is typically associated with mVOCs. More research is needed to determine the effects of mVOCs but some research suggests that mVOCs affect the eyes and URT Korpi, A., Kasanen, J.P., Alarie, Y., Kosma, V.M., Pasanen, A.L Sensory irritating potency of some microbial volatile organic compounds (MVOCs) and a mixture of five MVOCs. Environ. Health 1999; 54(5), P. 347-52. WHO. Guidelines for Indoor Air Quality: Dampness and Mould. WHO: Germany, 2009. . 

Damp Environments

Damp environments will have more than just mold. Where there are wet building materials, you will also find bacteria, insects, mites, rodents, and VOCs from failing building materials. The association with health effects is stronger when looking at the presence of dampness in general rather than narrowly looking just at mold. Perhaps there is a synergistic effect with all of these various organisms being together in an area of dampness.