The Cause

Mold and mildew: Mold and mildew grow where there is moisture, and odor-carrying bacteria can accompany them. This fast-growing ecosystem results in bad smells.
Bodily functions: The most natural odors can be the most embarrassing — especially if there is no bathroom window and you have a house full of guests.

The Cure

Mold and mildew: Clean off the bacteria that generate odors with Naturally Yours Mold & Mildew Remover ($5 a quart, 888-801-7347), and dry all tiles and caulking when wet. Lysol Disinfectant Spray ($4 at supermarkets) inhibits growth.
Bodily functions: Lit candles or matches kill odors, as does Lysol Disinfectant Spray. Urine can emit an ammonia-like odor, so clean the toilet regularly.