Mold!

When mold does take hold in your home, fight the temptation for a quick fix. "Address the source of the problem first and then deal with the mold growth," says Dr. Chew. "If you just paint over it, the front part of the wallboard may look fine, but if you look at the reverse side, inside the wall cavity, you could see the mold growing back," as in the image at left.

"I've done a lot of work with Katrina victims" she says, "and my fear is that even though they've done a lot of remediation, when you put up new sheet rock on wet wooden studs, the mold will just come back"—which means the troublesome stuff could be spreading through your home, releasing a high concentration of spores into the air you breathe, without your ever seeing it.