Now researchers at University College of London have quantified another health risk for those exposed to secondhand smoke: mental-health illness. In a study of 8,155 men and women, researchers documented a 50% greater risk of psychological distress in nonsmokers with the highest levels of nicotine residue in their blood, compared with those with the lowest levels.

Previous data have suggested a link between smoking and mood disorders, and nicotine exposure in animals is known to trigger depressive symptoms, stress, anxiety and a dampening of feelings of reward and satisfaction.Researches group extended those findings to nonsmokers who passively inhale cigarette smoke, and while the study does not establish that the exposure directly causes changes in mood, it does suggest a strong association.

What’s particularly worrisome is that for the majority of the population, even transient exposure to secondhand smoke is sufficient to have an effect; those with the lowest cotinine levels, equivalent to the amount that might be absorbed during occasional forays to a smoke-filled bar or restaurant, still increased their risk of depressive symptoms and anxiety by 25%, compared with those with negligible exposure.

The survey also revealed that most passive smoke exposure is occurring in the home. Thanks to aggressive legislation to ban smoking in public places, most smokers are lighting up at home, where nonsmokers, including children, are more likely to be exposed on a chronic and intense level. Passive smoke is very harmful, and if you smoke and live with a nonsmoking partner, we need to help them realize that they are not only doing themselves quite a lot of harm, but they could also be affecting people living with them.