D ark-colored substances located in wet and damp areas like basements and bathrooms are most likely mold or mildew. Mildew won't damage surfaces and is rarely a health problem. You can remove it with a combination of hot water and a household cleaner. Molds, however, are more troublesome. Some types of mold that thrive on damp walls and floors are toxic to people and pets, causing potentially serious respiratory infections.
Molds can also trigger allergies in susceptible people.
A ll molds belong to the fungus family-a diverse group of organisms that includes thousands of species ranging from mushrooms to the microbes that cause athlete's foot. In buildings, molds feed on drywall paper, wallpaper and wood. Molds are everywhere, but the moisture and generally poor ventilation in bathrooms and basements encourages their growth. Showers, sinks, washing machines and wall seepage are the major sources of moisture in these areas. The more infamous of the two is Stachybotrys, which is considered to be a toxin.