Smoking has been banned in most public places, based mostly on fears of second-hand health effects on the non-smokers around their tobacco-using peers.

But third-hand smoke – the residues that linger in dust and on surfaces – also increase lung cancer risk in mice, according to new research by scientists at the Lawrence Berkeley National Laboratory.

Young mice exposed to the toxic particles have increased incidence and severity of lung cancer later in life, according to the study in the journal Clinical Science.

“These data indicate that early exposure to (third-hand smoke) is associated with increased lung cancer risk,” write the researchers.

Previous studies had shown that the trace materials in third-hand smoke include a wide array of volatile and semi-volatile organic compounds, as well as known carcinogens including polycyclic aromatic hydrocarbons, and tobacco-specific nitrosamines, according to the Lawrence Berkeley team.

An experimental group of A/J mice – which have a tendency genetically to develop lung cancer – were exposed to these third-hand smoke particles between 4 and 7 weeks of age through cotton cloth used as bedding material, the scientists report. Twenty-four mice were exposed; 19 counterparts were a control group, they add.

The mice were then checked at 40 weeks of age – and the mice with exposure to the particles had increased rates of lung cancers, as compared to a control group of rodents, the scientists write.

In vitro models of culture human lung cancer cells showed that the exposure to third-hand smoke induced breaks in the DNA and increased cell proliferation and colony formation, according to the paper. Further RNA work showed a pathway through the p53 gene and its proteins, which act to suppress cancer formation, the paper adds.

“RNA sequencing analysis revealed that (third-hand smoke) exposure induced endoplasmic reticulum stress and activated p53 signaling,” the study authors write. “Activation of the p53 pathway was confirmed by an increase in its targets p21 and BAX.”

Third-hand exposure can occur through inhalation, ingestion, or through the skin – and normal cleaning methods do not remove the traces, the scientists add. The most susceptible people would be infants or young children who crawl on the ground or put objects in their mouths, according to the researchers.

However, understanding the real-world effects on a population would potentially be difficult, since most people exposed to third-hand smoke would likely be exposed to second-hand smoke as well, they write.

The research was funded by the University of California’s Tobacco-Related Disease Research Program, and the National Institute on Drug Abuse, among other agencies.