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Acne is a diabolically cruel thing: somehow it strikes your most visible feature just at the age when you become most vulnerable to a gaze. Not surprisingly, acne is often accompanied by serious depression among teenagers. In fact, a 1999 study found that kids with acne bad enough to prompt a trip to the dermatologist reported having emotional and social problems as severe as those reported by patients with disabling diabetes and epilepsy.

Other studies have shown similar, if less extreme, reactions to bad cases of acne. And so an international team of researchers — including scientists from Harvard Medical School in Boston and University Medical College in Tibet — decided the acne-depression question needed further investigation. The team's intriguing new paper, published this week in the open-access journal BMC Public Health, not only confirms that acne goes hand in hand with depression and anxiety but further suggests that teens' mental distress may in fact be worsening the condition of their skin.

Led by Jon Halvorsen, a dermatologist at the University of Oslo in Norway, the researchers launched their study in 2004, inviting every 18- and 19-year-old who was finishing high school in Oslo to answer some questions about zits and other things. Of the 3,659 students invited, 90% participated, along with 467 other 18- and 19-year-olds who were not graduating. The teenagers completed questionnaires about the severity of their acne as well as how much anxiety and depression they were experiencing, what they usually ate and whether they smoked and drank. Separately, the researchers collected socioeconomic data on the teens from the country's central information-gathering agency, Statistics Norway.

The results show that the level of mental distress kids reported was strongly associated with how much acne they said they had, independent of other factors like diet or lifestyle. Roughly 19% of all kids who reported symptoms of anxiety and depression said they had acne, compared to only 12% of those who reported no mental distress. Among boys, those with depression and anxiety were 68% more likely to report acne than their happier peers; among girls, those with mental distress were twice as likely as those without to report acne.

The study found, for the first time, a linear relationship between mood and pimples: the worse the mental-illness symptoms, the worse the acne. It's possible that the association simply means that kids who feel depressed are more likely to report they have bad acne, even if they don't — but previous studies have shown that dermatologists independently agree with teens' self-reports of acne severity about 75% of the time. Some of the depressed and anxious kids in the Norwegian study may have exaggerated their acne, but in a sample as large as this one, it's unlikely that most did.

So how could mental-health problems actually exacerbate acne? One theory is that people with mental distress eat more junk food. Dearly held teen lore says that overindulging in chocolate and potato chips — which can make greasy fingers and, consequently, greasy faces — spawns pimples. This is mostly myth, according to the study's findings, although they offered a bit of support for the notion that diet plays a role. Girls in the study who consumed few vegetables tended to have more zits than girls who ate lots of greens. But diet was entirely irrelevant for boys.

The authors also discount other lifestyle factors. The Norwegian adolescents who said they regularly use alcohol and cigarettes were no more likely to report acne than those who were abstemious. Only mental distress was strongly correlated with acne in both boys and girls.

But that still doesn't answer the question of what mechanism might be at work. The authors offer a few hypotheses. For instance, stress may somehow stimulate the growth of nerve fibers near sebaceous glands, which in turn contributes to the increased production of sebum — the fatty substance that combines with cell debris and dead skin cells to form those familiar blackheads and pustules. (All together now: Eww.) That theory is unproved, but previous research on the effects of depression and acne drugs suggests the authors may be onto something: we know, for example, that antidepressants can improve acne. We also know that a widely used drug that treats acne, Accutane (isotretinoin), has been associated with an increase in depression, although no causal link has been established.

The new study has some obvious shortcomings, particularly that it relies entirely on self-reports from a self-selected group of respondents. Much more rigorous research needs to be conducted to understand the relationship between mental illness and pimples — as well as the root cause of bad cases of acne. But in the meantime, drug companies might want to start working on a Clearasil-Prozac miracle cream.

• John Cloud