A naphthalene mothball takes many months to evaporate, while a para-dichlorobenzene mothball lasts about one month. Mothballs are used to repel insects that eat natural fibers, such as moths and silverfish, and keep them away from books or clothes. The mothballs' pungent smell goes away when they have fully evaporated.
The Environmental Protection Agency cautions that exposure to naphthalene mothballs can have detrimental health effects. If mothballs are eaten or their fumes are inhaled, they can cause sickness. Contact with the skin or eyes can cause irritation. The U.S. Department of Health and Human Services says that para-dichlorobenzene may cause cancer as observed in animal studies.