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. 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. Questions raised by molds interest Mike Muilenberg, research associate and instructor in the Department of Environmental Health at Harvard's School of Public Health. As part of a series of studies on indoor allergens, Muilenberg is looking at the relationship between mold and health.
