Everyone knows that secondhand smoke is bad for everyone, in particular kids, who can go on to develop serious physical ailments because of exposure to nicotine and tobacco products. But a new study suggests that the brains of young people are also vulnerable to the assaults of secondhand smoke, and that a smoky home can have lasting neurodevelopmental effects.

The researchers, who published their results in Pediatrics, write that “more than twofold-increased rates were observed in parent-reported childhood neurobehavioral disorders” in kids exposed to secondhand smoke at home compared with kids who hadn’t been exposed. The disorders with elevated risk include ADHD, disruptive behavior disorders, and learning disorders. They also found, according to a report in the Los Angeles Times, that secondhand smoke exposure was linked to a 50% greater probability that children would develop two or more of these illnesses.

The researchers caution that they have not identified a concrete causal relationship between secondhand smoke and childhood mental illness. And they don’t yet know exactly how they could be connected. But this study, coupled with research into the link between tobacco/nicotine exposure and physical illness, addiction, and anxiety, should give parents another reason to pause before lighting up at home.