It is accepted that other people's smoke is bad for your lungs and heart, and new research suggests it could be damaging your mental health, too.

Researchers found that non-smokers exposed to regular secondhand smoke were 50 percent more likely to suffer from psychological distress than those not exposed.

And their risk of being admitted to a psychiatric hospital over the next six years was nearly tripled (it was almost quadrupled for smokers).

So-called "passive smoking" is very common, Dr. Mark Hamer of University College London, one study found evidence of secondhand smoke in 60 percent of non-smokers. Exposure to secondhand smoke among non-smokers is determined using saliva levels of cotinine, which is formed when nicotine is broken down in the body.

To investigate, Hamer and his colleagues studied 5,560 non-smoking adults and 2,595 smoking adults, none of whom had a history of mental illness. Subjects answered questions about mental distress and admissions to psychiatric hospitals were tracked for six years.

A total of 14.5 percent of study subjects reported psychological distress. According to the study, the higher a person's secondhand smoke exposure, the greater their risk of psychological distress, while smokers were the highest risk.

The risk of hospitalization was 2.8 times greater for secondhand smokers compared to people not exposed to secondhand smoke, while it was 3.7 times greater for smokers.