Mike Muilenberg

Molds, those unpleasant-looking fungi that live on plant or animal matter, are at the center of a debate about health dangers posed by some species suspected of being toxic. Mold fears have prompted home abandonments and lawsuits: one family in Texas won a $32 million judgment last year against their insurance company for not addressing mold problems in their home; the family attributed several health problems to mold. A group of families in New York City filed an $8 billion lawsuit against their landlord because of mold-related problems in their homes. The suit was recently settled out of court. A Delaware woman received a $1 million jury award last year after claiming her health suffered from mold exposure in her apartment.

Molds are found in all kinds of environments. Estimates of the number of kinds of molds range from tens of thousands to more than 300,000, with more than 1,000 species known to typically grow indoors, according to the Centers for Disease Control and Prevention (CDC). While many molds appear to be benign to humans–and some, such as the kind that produces penicillin, are beneficial–several species are considered to be potent toxins.

"We in the Department of Environmental Health have been involved in indoor air studies for over 20 years and are aware that there are problems with fungal contamination indoors, in homes, and in office buildings," said Mike Muilenberg, research associate and instructor in the Department of Environmental Health, "but I think that some of the recent panic is a little bit out of proportion to the risk."

Scientists have been familiar for years with health problems posed by some molds. Aflatoxin, for example, from the mold Aspergillis flavus in peanuts, is a known carcinogen. As a result, the Food and Drug Administration and US Department of Agriculture monitor peanuts and field corn for aflatoxin levels and can prevent products from getting to the market if aflatoxin levels are too high.

A different mold, Stachybotrys chartarum, formerly known as Stachybotrys atra, is behind the recent spate of home abandonments and lawsuits. Scientists became aware of the dangers of ingesting the blackish mold more than 60 years ago after livestock ate large amounts of contaminated feed and suffered from internal bleeding as a result, said Muilenberg.

In the past few years, it has become known that S. chartarum in the right conditions grows on building materials with high cellulose and low nitrogen content such as wallboard, gypsum board, and cellulose ceiling panels. While the molds Cladosporium, Penicillin, Aspergillus, and Alternaria are common indoor molds, no one is sure how often S. chartarum infiltrates peoples’ homes. According to the CDC, a link between exposure to S. chartarum and health effects such as memory loss and pulmonary hemorrhaging remains unproven, despite the charges of some litigants.

Sensitivity to molds varies among individuals. Those with mold allergies or asthma may develop congestion or wheezing in the presence of mold; for severe asthmatics, this can be life-threatening. Individuals with suppressed immune systems may develop fungal infections after exposure to particular molds. The Harvard Six Cities Study suggested in the late 1980s that respiratory symptoms in elementary school-age children were strongly associated with mold, mildew, and dampness in the home. Other studies have produced similar findings.

As part of a series of studies on indoor allergens, Muilenberg is looking at the relationship between mold and health. In one project, he and his colleagues are following a group of children as they grow up, measuring their exposures to different allergens and their respiratory health at specific ages. Former doctoral student Paul Stark, who worked on the project, reported in his thesis that there may be a connection between fungal exposure and lower respiratory illness. The data is preliminary.

Muilenberg is also working with HSPH faculty members on a study of outdoor allergens, including fungi, and asthma.

Funding for mold research has been minimal. "Maybe that’s because funding agencies tend to question the relevancy," said Muilenberg. Private consultants more than government-funded scientists are conducting much of the current indoor air sampling in buildings, he said.

"In a normal, or even slightly contaminated, office or home environment, the levels reported so far have not been high enough to see any type of health effect that could be attributed to the fungal toxin," said Muilenberg. "Effects on the immune system and symptoms such as headaches and dizziness have been reported, but that was after very high exposures to S. chartarum."

In addition to nutrients, S. chartarum needs a constant source of moisture to grow. HSPH doctoral student Susan Doll recently showed in her thesis that materials on which the mold grows need to be wet–having humid air alone will not prompt growth. Leaky plumbing or dripping condensation are common sources of wetness for mold growth.

"You have to solve the moisture problem," said Muilenberg. "Eliminate whatever is causing surfaces in the home to get wet. Clean-up after that depends on how extensive the mold infiltration is. Usually wiping down surfaces with diluted bleach will kill the mold on the surfaces and keeping the surfaces dry afterwards will prevent further growth."

Other items may not be so easy to clean up. Contaminated carpeting is a real problem, said Muilenberg, because treading and vacuuming kick up spores into the air.

"I think if you have a carpeted floor that’s been wet and not dried out immediately, and it smells musty, get rid of the carpet," he said.

Testing to see what kind of mold is growing in a home is not usually necessary, according to the CDC. The agency suggests getting rid of any mold growth.

Muilenberg said that, generally speaking, more research into the relationship between mold and health effects needs to be done.

Keep the humidity level in the house below 40 percent.