The 18-year-old French woman was hospitalized with scaly skin on her legs and hands, appearing unsteady and mentally sluggish, doctors said.
They found the condition puzzling, especially because the woman's twin sister displayed similar, but less severe, symptoms and there was no family history of the problem, the doctors reported in the June 27 issue of the New England Journal of Medicine.
Several days later, doctors discovered the cause: a bag of mothballs stashed in her hospital room.
The teenagers had been using the mothballs to get high, inhaling air from the bag for about 10 minutes a day because classmates had recommended it.
The sicker of the young women also had been chewing half a mothball a day for two months.
The doctors described the high as "dangerous" and most likely under-reported in medical literature.
The teenager told the doctors that she continued to use the mothballs during her hospitalization "because she thought her symptoms were not related to her habit," said Lionel Feuillet at the Hospital of Timone in Marseille, France.