Third-hand smoke - tobacco residue that persist in houses, apartments and hotel rooms after smokers move out - may be just as deadly as first-hand or second-hand smoke, a new study has claimed.
"Do not smoke and do not allow yourself to be exposed to smoke because second-hand smoke and third-hand smoke are just as deadly as first-hand smoke," said a scientist from the University of California, Riverside who led the first animal study of the effects of third-hand smoke.
While first-hand smoke refers to the smoke inhaled by a smoker and second-hand smoke to the exhaled smoke and other substances emanating from a burning cigarette that can get inhaled by others, third-hand smoke is the second-hand smoke that gets left on the surfaces of objects, ages over time and becomes progressively more toxic.
"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, a professor of cell biology who led the study.
"We found significant damage occurs in the liver and lung. Wounds in these mice took longer to heal. Further, these mice displayed hyperactivity," said Martins-Green.
Third-hand smoke is a potential health threat to children, spouses of smokers and workers in environments where smoking is, or has been, allowed, researchers said.
Contamination of the homes of smokers by third-hand smoke is high, both on surfaces and in dust, including children's bedrooms.
Re-emission of nicotine from contaminated indoor surfaces in these households can lead to nicotine exposure levels similar to that of smoking, researchers said.
Third-hand smoke, which contains strong carcinogens, has been found to persist in houses, apartments and hotel rooms after smokers move out.
Researchers found that the mice exposed to third-hand smoke in the lab showed 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, third-hand smoke was found to increase lipid levels and non-alcoholic fatty liver disease, a precursor to cirrhosis and cancer and a potential contributor to cardiovascular disease, researchers found.
In the lungs, third-hand smoke was found to simulate excess collagen production and high levels of inflammatory cytokines (small proteins involved in cell signalling), suggesting propensity for fibrosis with implications for inflammation-induced diseases such as chronic obstructive pulmonary disease and asthma, they said.
In wounded skin, healing in mice exposed to third-hand smoke showed many characteristics of the kind of poor healing observed in human smokers who have gone through surgery.
The study appears in the journal PLOS ONE.