Proper use of mothballs involves the fumes building up in airtight containers to kill the insects inside. Mothball product labels also direct users to avoid skin contact and to use gloves when handling mothballs.
Usage of mothballs outside of airtight containers can lead to people breathing in toxic fumes, causing coughing, wheezing, headache, nausea, vomiting and disorientation. These conditions often affect people with a history of impaired respiratory function.
Mothballs don't affect all insects the same say. Naphthalene, which is the active ingredient of mothballs, has no visible adverse effect on the Formosan subterranean termite. In fact, these termites mix the chemical into the insulation layer of their tunnels to keep ants, fungi and nematode worms away.