Third-hand Smoke as Deadly as Second- and First-hand

Third- and second-hand smoke are as deadly as first-hand smoke, a new study led published in the journal PLOS One suggests.

First-hand smoke refers to what is inhaled by a smoker and second-hand smoke to the exhaled smoke as well as other substances emanated from a burning cigarette that can be inhaled by others.

Third-hand smoke, meanwhile, refers to smoke left on surfaces of objects and becomes more toxic as it ages. Contamination of this type is high in the homes of those who smoke, posing a risk to spouses and children, the researchers warned. What's more, re-emission of nicotine from contaminated surfaces can lead to nicotine exposure levels similar to that of smoking.

"We studied, on mice, the effects of third-hand smoke on several organ systems under conditions that simulated third-hand smoke exposure of humans," Manuela Martins-Green, a professor of cell biology at the University of California, Riverside, said in a statement.

The results showed "significant damage" to the liver and lungs, with wounds in the mice taking longer to heal.

"Further, these mice displayed hyperactivity," said Martins-Green, who led the study.

Excrement from the mice revealed levels of a tobacco-specific carcinogen that resembled those found in children faced with second-hand smoke exposure.

"More recently we have found that exposure to third-hand smoke results in changes that can lead to type II diabetes even when the person is not obese," Martins-Green said.

"There is still much to learn about the specific mechanisms by which cigarette smoke residues harm nonsmokers, but that there is such an effect is now clear," she added. "Children in environments where smoking is, or has been allowed, are at significant risk for suffering from multiple short-term and longer health problems, many of which may not manifest fully until later in life."