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Mold problems in Schools

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Mold (fungi) are organisms which play a vital role by decomposing old food, plants and wood. Low to moderate levels
of molds are commonly found in the air and on soil, dust and surfaces both indoors or outdoors. Indoor mold growth is
especially common in areas with water damage.

High concentrations of mold can cause health problems by 3 mechanisms: 1) They produce hundreds of allergens which can worsen asthma and allergies. Many studies have linked high levels of indoor or outdoor molds in air or dust with significantly higher levels of asthma in infants, children and adults. 2) Molds produce a wide range of toxic chemicals called mycotoxins which can damage the kidneys, nerves, respiratory and immune systems and cause cancer, and 3) Molds (fungi) can cause infections. Molds such as Candida and Aspergillus frequently cause life threatening infections in patients with compromised immune systems such as those with HIV/AIDS, cancer, are badly malnourished or on immune suppressing drugs (Curtis, 2004).


Children spend about 30 to 40 hours per week in schools. About one quarter of all US school buildings have mold or moisture problems or need extensive repairs (Moglia 2006). Both new and old school buildings can have health related problems. In large cities, many schools are over 75-100 years old and frequently have problems with dust, peeling paint/plaster, and water damage. Newer school buildings frequently have problems with inadequate outdoor ventilation, off gassing of chemicals from building materials and buildup of moisture during certain climate conditions. Animal pests such as cockroaches, rats/mice and pigeons are often found in schools and can worsen asthma and allergies. The pesticides used to treat these pests can also worsen asthma and allergies, cause cancer and cause neurological symptoms like headaches, fatigue and poor concentration.

Such school building related problems are especially concerning for the estimated 6.1 million children with asthma. Asthma and allergies are estimated to cause 18 million lost school days annually in the USA alone. Several studies have reported that visible mold and moisture damage are associated with significantly higher levels of asthma in schoolchildren. Mold/water damage and heavy visible growth of molds such as Aspergillus and Stachybotrys are associated with life threatening lung hemorrhage in children younger than 2 years.

Water and mold related problems in schools sometimes become big issues which involve parents, school administrators, press and politicians. The author has experience working with many mold and indoor air problems in schools in Illinois, Wisconsin, Indiana, Ohio and New York. Sometimes a major mold/ water damage issue is found, and other times no mold problem is found and other indoor air quality issues come into play.

If several members of the school are experiencing new health related problems such as asthma, sinus problems or severe fatigue, obtaining medical documentation (with the consent of the students or parents) can often be helpful both in conducting health investigations and in convincing school administrators that the health problems are probably related to building conditions.

Oftentimes schools have day care centers for infants and toddlers. Children under 2 years of age are especially vulnerable to the health effects of mold and bacteria since their lungs and immune systems are not fully developed. Special care needs to be taken to insure good air quality in day care centers.


Excessive growth of mold and bacteria in schools is usually caused by water or moisture problems. The limiting factor for growth of most molds is not food but water. Water damage in schools is commonly produced by leaking pipes/ sinks/ toilets, and outdoor flooding which creeps indoors. Excessive humidity and water condensation can also develop in indoor pools, greenhouses, kitchens, and laundry rooms. High indoor humidity from outdoors can also stimulate mold growth. Schools should use dehumidifiers and air conditioners in hot or humid climates. Tornados and hurricanes can also flood schools. Many molds can grow quickly and can cover large areas in a one day to one week period.

Mold can grow on many surfaces indoors including wood, paper, books, drywall, carpets, ceilings, floors, walls, foods, clothes, plants and dust.  Mold often emits a musty or yeasty odor. Oftentimes mold grows in visible patches that are easily seen and photographed. Other times significant levels of mold can grow without any visible patches of fungi.

What should parents, teachers or school personnel do if they suspect a mold problem in their school? The first step should be to identify any areas of water/moisture damage, visible mold growth, or stronger musty or decaying odors. Any areas of visible water damage or visible mold growth should be photographed to show to school administrators or maintenance personnel.  

Any sources of water leakage should be fixed within 24 hours to prevent mold and bacteria growth. Non porous surfaces like plastic, metal, treated wood, ceilings, walls or floors  should be wiped off with detergent water or a dilute bleach solution and dried with rags, towels and fans. If a bleach solution is used it should be used only in areas with good outdoor ventilation. Bleach should NOT be used with ammonia or production of toxic phosgene gas may result. Use of dehumidifiers are often useful in cleaning up a school building.  Cleanup of a large water/ moisture problem may require a professional cleanup crew.

Porous items like furniture and carpet require special treatment such as steam cleaning followed by drying.  Some water damaged items like books, papers and paintings may require professional remediation to save. Some wet items may have to be thrown out if they are soggy and have developed heavy mold growth or a musty smell. Water damage in walls, ceilings, floors and drywalls can be checked for water/mold problems with such devices as moisture meters, infrared meters and fiberoptic viewing devices. Use of humidity monitoring gauges may be useful in preventing moisture problems in the future.


Many industrial hygienists and environmental firms offer sampling for molds in the indoor environment. Indoor mold testing can be helpful, although it can be fairly expensive if a big and detailed study is done. If heavy visible mold growth is visible to the eye, the school certainly has a mold problem and probably does not need extensive mold testing prior to cleanup.  Testing for molds after cleanup can be helpful in determining that an adequate cleanup has been conducted. Extensive mold testing can be useful in cases where the school has health problems suspected to be mold related but no obvious source of mold is found.

There are a number of ways to test for the presence of mold in buildings, including the testing for viable (living) and non viable spores, testing for fungal DNA and testing for mold toxins (mycotoxins). A good mold study should involve testing for molds in both the air and on surfaces/ dust. In some cases, trained dogs have been used to detect mold growth by their keen smell.

There are no official standards for levels of mold in either air or in dust/ surfaces. Some studies suggest that indoor levels of mold above about 1,000 spores per cubic meter can cause worsen asthma and nasal problems. However, outdoor mold levels can often exceed 1,000 spores per cubic meter of air in hot and humid weather. Lower levels of certain toxic molds like Stachybotrys or Fusarium can cause health related problems at spore levels well below 1,000 spores per cubic meter of air. Airborne levels of mold above 10,000 spores are probably harmful to every persons’ health and levels above 100,000 spores per cubic meter are definitely harmful to health.


Other factors besides mold can cause significantly indoor air problems in schools. Newer schools sometimes have inadequate outdoor air ventilation rates. Inadequate outdoor ventilation has been linked to more asthma and more respiratory infections among students. Outdoor ventilation can be increased by opening more windows or opening more vents in forced air ventilation systems. Pesticides, cleaning solvents, lead, asbestos and pests like cockroaches, mice/rats and pigeons can all cause significant indoor air quality related issues in schools.

PS Luke Curtis MD, MS, CIH has an MD degree and an MS in public health. He has 21 years experience in working with mold and indoor air quality problems. He has published 71 medical journal papers- including 14 on mold, bacteria and infection control. Luke welcomes questions/comments and can be reached at

Luke Curtis, Alan Lieberman, William Rea, Martha Stark and Marsha Vetter.  Adverse Health Effects of Indoor Molds. Journal of Nutritional & Environmental Medicine 2004;(3):261-74.
Moglia D, Smith A, MacIntosh D, Somers J.  Prevalence and implementation of IAQ programs in US Schools.  Environmental Health Perspectives  January 2006; 114(1):141-6.

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