Mold is a fungus that grows fuzzy or downy when spores get wet and that eats the things it rests on. To control mold, you have to control moisture. Cleaning up mold without fixing a water problem solves nothing. And moisture has to be removed quickly.

You should suspect hidden mold if a building smells moldy or if there was water damage and people now complain of health problems. It can be on the back of drywall, wallpaper or paneling, on top of ceiling tiles, under carpets and pads, inside walls or around pipes, for instance.

The Environmental Protection Agency provides key facts about mold. Among the highlights:

• Mold is part of the natural environment, helping break down organic matter such as dead wood and leaves. It grows indoors when mold spores (which are everywhere, even in dust) land on wet surfaces. Without moisture, mold can't grow.

• Keep indoor humidity below 60 percent. If moisture collects on surfaces like windows or pipes, dry it immediately and address the source.

• Allergic reactions to mold are common. Mold can also trigger asthma attacks and cause other health problems.

• If you have mold, move fast. You can do your own cleanup on a patch less than about 3 feet by 3 feet. Bigger than that, you should get help.

• If you suspect the heating/ventilation/air conditioning system is contaminated, don't run it until you get the mold cleaned up. It will just spread it.

• If the water or mold damage was caused by sewage, get professional help.

• To clean up mold, fix the water problem first and dry everything completely. Then scrub mold off hard surfaces with detergent and water and dry completely.

• Don't inhale it while you're cleaning. You may need to throw away carpets or other porous materials that have mold.

• Never paint or caulk over mold. It's likely to peel, and mold grows and feeds quite happily on some paint.

• You can get an inexpensive N-95 respirator to wear while cleaning mold to avoid inhaling it. You should wear gloves and goggles.

• Always check back to see that the mold site shows no more signs of water damage or mold growth.

• If you believe you have a hidden mold problem, be careful. Taking wallpaper off, for instance, can release tons of spores. Consider hiring a professional.