Molds are fungi that can be found both indoors and outdoors. No one knows how many species of fungi exist but estimates range from tens of thousands to perhaps three hundred thousand or more. Molds grow best in warm, damp, and humid conditions, and spread and reproduce by making spores. Mold spores can survive harsh environmental conditions, such as dry conditions, that do not support normal mold growth.
Molds are found in virtually every environment and can be detected, both indoors and outdoors, year round. Mold growth is encouraged by warm and humid conditions. Outdoors they can be found in shady, damp areas or places where leaves or other vegetation is decomposing. Indoors they can be found where humidity levels are high, such as basements or showers.
Some people are sensitive to molds. For these people, exposure to molds can cause symptoms such as nasal stuffiness, eye irritation, wheezing, or skin irritation. Others, such as those with serious allergies to molds or those exposed to large amounts of mold in occupational settings, may have more severe reactions —including fever and shortness of breath. Some people with chronic lung illnesses, such as obstructive lung disease, may develop mold infections in their lungs.
Recent studies have suggested a potential link of early mold exposure to development of asthma in some children, particularly among children who may be genetically susceptible to asthma development, and that selected interventions that improve housing conditions can reduce morbidity from asthma and respiratory allergies, but more research is needed in this regard.
Mold growth, which often looks like spots, can be many different colors, and can smell musty. If you can see or smell mold, a health risk may be present. You do not need to know the type of mold growing in your home, and CDC does not recommend or perform routine sampling for molds. No matter what type of mold is present, you should remove it. Since the effect of mold on people can vary greatly, either because of the amount or type of mold, you can not rely on sampling and culturing to know your health risk. Also, good sampling for mold can be expensive, and standards for judging what is and what is not an acceptable quantity of mold have not been set. The best practice is to remove the mold and work to prevent future growth.
While the Center for Environmental Health can address mold issues from a sanitation perspective in the facilities we inspect, such as restaurants and hotels, we do not have the authority to address mold issues in other businesses, private residences, or rental properties. We do offer resources that may be able to assist you in resolving mold issues in these types of structures on our Resources for Non-EH Program Complaints page.