A new study conducted on mice suggests that so-called “third-hand smoke” might be as dangerous as second-hand smoke.

While second-hand smoke is the smoke that is exhaled by smokers and that is released by burning cigarettes, third-hand smoke refers to the smoke that clings to objects and fabrics for long afterward and typically leaves behind the tell-tale odour smoking.

Scientists say this third-hand smoke can accumulate on surfaces and in house dust and age over time, becoming progressively more toxic with carcinogens.

Researchers at the University of California, Riverside, recently completed a study on mice to better understand the effects of third-hand smoke on several of the mice’s organ systems.

For six months, the mice lived in ventilated cages containing materials that had been exposed to second-hand smoke.

Manuela Martins-Green, a professor of cell biology who led the study, says at the end of the six months, her team found significant damage in the mice’s livers and lungs, such as higher fat levels in their livers.

Wounds in the mice also took longer to heal, similar to the kind of poor healing seen in human smokers who have gone through surgery.

And, in behavioural tests, the mice exposed to third-hand smoke also showed signs of hyperactivity.

The research team says the mice also excreted levels of a tobacco-specific carcinogen similar to those found in children exposed to second-hand smoke.

The study results appear in PLoS ONE.

Martins-Green says the results of the study suggest that more research is urgently needed on the effects of third-hand smoke in humans.

“There is still much to learn about the specific mechanisms by which cigarette smoke residues harm non-smokers. But that there is such an effect is now clear,” she said in a statement.

Her team notes third-hand smoke has been found to persist in houses, apartments and hotel rooms long after smokers move out.

The team says its results suggest that children in environments where smoking has been allowed are at “significant risk” for suffering from multiple health problems, "many of which may not manifest fully until later in life."