Mothballs emit one of the most distinctive and unpleasant household scents. Since moths will chew holes through clothing or other textiles, people pack away these stinky repellents to kill any moths that attempt to. But as they convert from a solid to a gas, you do not want to inhale too much of it. The U.S. Environmental Protection Agency even requires mothball manufacturers to include a warning on packaging to "avoid breathing in the vapors."
Studies on one active ingredient in some repellents, paradichlorobenzene, found that it can cause cancer in animals [source: EPA]. Although scientists do not know if it is also a human carcinogen, the animal trials provided sufficient evidence to urge people to handle them with caution. Other types of moth balls use naphthalene, which after prolonged exposure can damage or destroy red blood cells [source: Centers for Disease Control and Prevention]. The chemical can also stimulate nausea, vomiting and diarrhea.
If you must use mothballs, put them in a sealed container in an area with separate ventilation from the rest of your house [source: EPA]. Also, wash any clothing that has been stored with mothballs before wearing it since the vapors will have absorbed into the fibers. For a safer, natural alternative, cedar chips should work as well.