Most Mothballs contains an active ingredient, and the active ingredient may be either naphthalene or paradichlorobenzene.
Each active ingredient can cause different health effects if the exposure is high enough. Mothballs slowly turn from solids to toxic vapor. When you smell mothballs, you are inhaling the insecticide.
Mothballs can also be dangerous if they are chewed or eaten. Children, pets and wildlife may mistake them for food or candy and eat them. One mothball can cause serious harm if eaten by a small child.
Therefore we should consider safer natural alternatives such as Camphor wood.
To read more about the article: http://npic.orst.edu/ingred/ptype/mothball/health.html