It turns out that it's not just second-hand smoke that you need to worry about. Third-hand smoke can also be an issue, and is just as deadly as first-hand smoke.

First-hand smoke refers to the smoke that's actually inhaled by a smoker. Second-hand smoke, in contrast, refers to the exhaled smoke that others may breathe in. Third-hand smoke is actually the residue from second-hand smoke that may be left on the surfaces of objects. For example, it's the aging substance that gets left on sweaters or clothes.

In order to assess the effects of third-hand smoke, the researchers took a look at mice. More specifically, they looked at how organ systems were impacted in these rodents.

"We studied, on mice, the effects of third-hand smoke on several organ systems under conditions that simulated third-hand smoke exposure of humans," said Manuela Martins-Green, one of the researchers, in a news release. "We found significant damage occurs in the liver and lung. Wounds in these mice took longer to heal. Further, these mice displayed hyperactivity."

The main issue is that as third-hand smoke settles and ages, it becomes progressively more toxic. The researchers found that the mice had alterations in multiple organ systems and excreted levels of a tobacco-specific carcinogen similar to those found in children exposed to second-hand smoke. In the liver, the smoke increased lipid levels and non-alcoholic fatty liver disease. In the lungs, the third-hand smoke simulated excess collagen production and high levels of inflammatory cytokines.

"The latter data, combined with emerging associated behavioral problems in children exposed to second- and third-hand smoke suggests that with prolonged exposure, they may be at significant risk for developing more severe neurological disorders," said Martins-Green in a news release.

In fact, research shows that children living with one or two adults who smoke in the home are absent 40 percent more days from school due to illness than children who do not live with smokers.

The findings are published in the journal PLOS One.