Mold forms wherever there is chronic moisture, like summertime condensation in the basement or wintertime condensation on windows and the northeast and northwest corners of some rooms. Mold is constantly sending out spores as it reproduces. These spores are what can aggravate or even cause asthma in some people. The problem is that these spores, invisible to the naked eye, float very lightly and can take hours to reach the floor-and are constantly stirred up every time you walk across the room.You must not let mold live in your house. You must kill it and wash away the dead material. Use a one-to-one mixture of standard laundry bleach and water with a little dishwasher soap. The bleach will kill the mold and the soap will clean off the wall. If it is heavy, wear a protective mask to not breathe a concentration of spores. If you have moldy furniture or books that are difficult to clean, throw them away. Just airing them out will not eliminate spores that will lie dormant waiting for a bit of moisture to grow again.