Molds found in nature are important in the breakdown of dead organic matter. Mold in the air, even indoors, is common, but in large quantities can be harmful to your health and begin to damage your furnishings. You or someone in your family may be allergic to even small amounts of mold. Mold grows on wet surfaces, so the best places to check are around water pipes and other surfaces constantly exposed to moisture. Check the insides of walls and ceilings, which can provide a moist breeding ground for mold in the event of a roof or plumbing leak.