Second-hand smoking has been associated with a range of physical health problems and new research now suggests that it might be linked to an increased risk of psychological problems too. Researchers from University College London studied 8,155 people in Scotland who took part in the Scottish Health Survey in 1998 or 2003. They filled out a questionnaire about their mental health problems and admissions to psychiatric hospitals were checked over six years of follow-up. Exposure to second-hand smoke was assessed by measuring levels of cotinine - a by-product of the breakdown of nicotine - in saliva. Non-smokers who had a high level of exposure to second-hand smoke had higher odds of mental distress. Smokers and non-smokers with a high level of of exposure to second-hand smoke were both more likely to be hospitalized for depression, schizophrenia, delirium or other psychiatric conditions.