A microorganism and type of fungus, molds are part of the natural environment and can be found everywhere, outside and indoors. Mold thrives in wet places. It can form on damp materials—outside on decaying organic matter like leaves, and inside, for example, on the paper face of wet drywall.
People come in contact with molds every day. Mold spores and fragments can get into the air we breathe. You may touch mold through household or occupational activities. Some mold may grow on food.
Of the many species of mold, most are not harmful. Certain molds are used to make foods, such as blue cheese, or medicines, such as penicillin. Some molds are harmful, producing substances called mycotoxins.
Mold and mildew are related, but different, types of fungus. Both require moisture. Mildew is typically powdery and lives on surfaces, whereas mold tends to be fuzzy, thicker, and greenish or black in color.
Health effects of mold
Health-related reactions in people depend on mold type, the amount and duration of exposure, and individual characteristics.
Events, such as floods or leaky pipes, can lead to mold growth indoors and to public concern about potential health effects. Researchers have discovered relationships
between some mold exposures and human health. Although not all species of molds have been studied, scientists have discovered health effects in people exposed to moldy environments.
The World Health Organization, National Academy of Medicine, and National Toxicology Program (NTP) all confirm that occupants of damp, moldy buildings have an increased chance of respiratory problems, such as shortness of breath and worsening asthma.
Asthma is a chronic airway disease characterized by inflammation. Exposure to mold and dampness indoors is associated with increased risk of developing asthma in young children, and more severe asthma in people who have the disease.
Aspergillus fumigatus, a common mold, may cause fungal asthma and result in airway obstruction caused by mucus overproduction. Repeated exposure to an allergen, particularly mold, may lead to asthma development.
Many studies show that mold exposure can worsen asthma symptoms, especially among young children. Some examples of findings follow.
- Infants who live in moldy homes were three times more likely to develop asthma by age 7.
- Babies exposed to mold were more likely to have asthma as young children.
- Some children may be exposed to mold in school, which can cause significantly more asthma symptom days than in school children who were not exposed.
Other health conditions
Allergic reactions to molds are the most common health effects in people, including symptoms such as runny nose, sneezing, coughing, and wheezing. People without allergies, but who are exposed to mold, likewise may experience symptoms, including eye irritation, sore throat, congestion, skin rash, and headaches.
Not everyone who comes in contact with mold will experience symptoms, and most people will have only minor symptoms such as a runny nose.
Inflammation and immune system changes may be caused by long-term exposure to mycotoxins. A type of mycotoxin, aflatoxins may be found on corn and other grain, seed, or nut crops. The NTP lists aflatoxins as a human carcinogen, and human studies have found a link between alflatoxins and increased risk of liver cancer.
Indoor concentrations of pollutants, such as mold, tend to be higher in low-socioeconomic status households. For example, their homes may have inside water leaks, a predictor of mold and moisture development. Research also shows that some low-income multifamily units may have low air exchange rates and inadequate ventilation, leading to higher exposure to mold allergens.
Native Americans living in tribal housing in areas, such as North Dakota and Alaska, may be particularly vulnerable to mold exposure. Mold is also found in tribal homes in warmer climes, including California, Arizona, and New Mexico.
Climate change and extreme weather
Climate change is a concern for mold spread because conditions inside buildings are influenced by the environment outside them. Building deterioration may result from extreme weather events, increasing the likelihood of mold growth. Under climate change, allergenic mold levels may rise through increased indoor dampness and warmer Temperatures
NIEHS supported the Head-off Environmental Asthma in Louisiana (HEAL) study, following Hurricane Katrina. This storm led to high levels of mold and other allergens, and disrupted health care for children with asthma. HEAL tested an asthma intervention that combined counseling and environmental changes. It successfully decreased the number of symptomatic days in children from 6.5 days to 3.6 days over 12 months. This type of intervention is still used.
Avoiding or controlling mold
Controlling moisture is the best way to control mold growth indoors. One way is through properly functioning HVAC systems with humidity control. Using fans and opening windows may also help dry out indoor spaces. Small mold spots can be removed with household cleaning solutions.
Consult experienced and qualified professionals for major mold cleanup projects.