BOSTON, Massachusetts (Reuters) -- 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 since the woman's twin sister displayed similar, but less severe, symptoms and there was no family history of the problem, the doctors reported in this week's New England Journal of Medicine that

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.

Mothballs, used to prevent moth larva from getting into clothing, contain paradichlorobenzene, a substance also found in air fresheners and insect repellents that can cause liver and kidney failure, and severe anemia.

The discovery comes at a time when teenagers are increasingly experimenting with legal drugs such as OxyContin, widely known as "hillbilly heroin," and Vicodin, often bought online or taken from medicine cabinets, even before trying marijuana or alcohol, health officials say.

The sicker of the women took six months to recover fully. Her twin, who had only been "bagging" for a few weeks, recovered after three months.

Feuillet told Reuters that a cleaning lady discovered the mothballs in the drawer of the patient's night table.

When the woman was asked what she was doing with the bag, "she showed us how she used to breathe directly into the mothballs bag," Feuillet said.

Although only three cases of getting high with paradichlorobenzene have been reported in medical literature, "since young people usually deny practicing self-intoxication, the incidence of this type of recreational activity is probably underestimated," Feuillet and his colleagues said in the Journal.