Third-hand smoke: Touching a smoker’s clothes can raise cancer risk, study warns

The dangers of secondhand smoking have been known for decades, but now scientists are warning about a new threat — thirdhand smoke.

A study in the US found even just handling a cigarette smoker’s clothing is enough to expose people to dangerous levels of cancer-causing chemicals.

Secondhand smoke is when exhaled fumes or the smoke from the end of a cigarette is breathed in by someone else.

Thirdhand smoke forms when particles from a cigarette seep into materials like hair, clothes and furniture and carpets.

Government researchers at the Berkeley Lab in California carried out a series of experiments on humans and mice.

In one study, three volunteers who did not smoke were asked to wear the clothes of a heavy cigarettes user for three hours.

Tests showed they had up to 86 times higher levels of toxic compounds known as NNK and NNN in their urine after the experiment.

In another study, researchers exposed the same chemicals to human lung tissue and showed they can cause DNA damage — which is one of the triggers of cancer.

Secondhand smoking is thought to increase the risk of lung cancer in non-smokers by 20 to 30 per cent, according to a US Surgeon General report in 2006.

But less is known about the dangers of thirdhand smoke, with fewer studies conducted in the area.

The Government-run Berkeley Lab in California team first identified how smoking leaves microscopic toxic chemicals on surfaces in 2010.

Previous studies have linked NNK — one of the carcinogens found in thirdhand smoke — can cause lung, liver and pancreas cancers. 

But now they have shown the ‘potential health impacts of thirdhand smoke’ for the first time.

The latest study was published in the journal Environmental Science and Technology.

Mice were exposed to doses of NNK and NNN, another carcinogen found in tobacco, on their skin.

Urine tests showed high levels of both the chemicals in their system, suggesting skin contact can lead to the compounds getting into their bodies.

Even after the team stopped exposing the mice to the chemicals, they continued to build in their bodies for another week.

They then tested how the chemicals interact with human lung cells in the lab to see how likely they are to cause cancer.

Contact with the chemicals led to DNA damage — the critical factor in cancer development that leads to tumours forming. 

Researchers asked people to wear cotton swabs and plasters for eight hours and then tested how exposure to the chemicals interacted with sweat left on them.

These were compared to dry samples. The samples were put in air locked tubes and exposed to the chemicals before being tested.

They found those that those that had been worn had higher levels of the compounds on the surface left over.

Lead author Dr Xiaochen Tang, a researcher at the Berkeley Lab, said: ‘Nicotine is released in large amounts during smoking, and it coats all indoor surfaces, including human skin.

‘We found that the presence of skin oils and sweat on model surfaces led to a higher yield of TSNAs.’ 

They asked three volunteers to long-sleeved shirts and full-length trousers that had been exposed to cigarette smoke for 30 days.

The concentrations of smoke in the clothing were similar to if they had been living in a home where someone smokes 20 cigarettes.

The volunteers did not use tobacco or cannabis in their day-to-day lives and weren’t exposed to smoke at home or work.

They were given the clothes to wear for three hours and asked to exercise for half an hour every hour so that they would sweat.

The experiment was done in a room where the air was recycled  nearly once a minute, to ensure the chemicals were being absorbed through the skin rather than volunteers breathing them in.

Urine tests were taken before the experiment and eight hours afterwards to measure levels of NNK and NNN in their systems.

They found levels of the chemical were 86 times higher in the samples taken after wearing the chemicals.

Researchers said it suggested that the chemicals pass through the skin into the bloodstream. 

Finally, they measured the levels of NNK and NNN in the air of 37 smokers homes and 19 nonsmoker homes.

The found smokers’ homes had more than the ‘no-significant risk levels’ set out by California’s Office of Environmental Health Hazard Assessment.

Levels were negligible in non-smokers homes. 

Author Professor Neal Benowitz, a medic at University of California, San Francisco, said: ‘These findings illustrate the potential health impacts of thirdhand smoke, which contains not only TSNAs but hundreds of other chemicals, some of which are also known carcinogens.

‘Next steps for this research will explore in more detail the mechanisms of adverse health effects associated with tobacco and cannabis residues, effective remediation strategies, and translation of scientific findings to tobacco control practice.’