New evidence shows that thirdhand smoke, or “residual chemicals left on indoor surfaces by tobacco smoke,” could be harmful, according to The Washington Post. Research suggests that tobacco residue can be “absorbed through the skin, ingested and inhaled months and even years after the smoke has dissipated,” the report says. Two studies suggested that thirdhand smoke increased the risk of lung cancer, liver damage, and diabetes in mice. Studies also suggested that smoke residue remains on floors and walls months after people no longer smoked in that area, and that smoking residue can seep into non-smoking areas and become airborne again in air-conditioning systems. In reaction to the growing research, the American Academy of Pediatrics issued a warning last year about the potential risks of thirdhand smoke.