"Where there's secondhand cigarette smoke," reports Bruce Bower in Science News, "there’s emotional fire." According to researchers at University College London, people exposed to large amounts of secondhand smoke — which is already linked to asthma, Sudden Infant Death Sydrome, and other conditions — are far more likely to develop psychiatric problems than those who live relatively smoke-free. (Watch a report about the effects of secondhand smoke.) Here, a concise guide to the findings:

What are the risks of psychological side-effects?
Over the six year study of 5,560 non-smoking adults and 2,595 smoking adults — none of whom reported previous mental health problems — the research team found that non-smokers with high exposure to secondhand smoke were 62 percent more likely to report psychological distress than unexposed test subjects. It gets worse: Follow-up interviews revealed that secondhand smokers were almost three times more likely to be admitted to a psychiatric hospital than nonsmokers.

How does cigarette smoke affect mental health?
While little is known about nicotine's relationship to specific mental disorders, studies suggest that the drug alters mood by interfering with hormone regulation, immune system responses, and the transmission of dopamine, one of the "chemical messengers" in the brain that's linked to depression.

How conclusive is the study?
Epidemiologist Dr. Mark Hamer, who led the study, says that, while such studies can't prove causality, "the link remained even after he and his colleagues accounted for social status, alcohol intake and other factors that could influence both the risk of mental health problems and the likelihood of being exposed to secondhand smoke."

Sources: U.S. News, Reuters, News Inferno