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 carcinogens to human lung tissue and showed they can cause DNA damage — which is one of the triggers of cancer.
US researchers say just handling a smoker’s clothing is enough to put them at risk 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.
But now they have shown the ‘potential health impacts of thirdhand smoke’ for the first time.
WHAT IS ‘THIRDHAND’ SMOKE?
Thirdhand smoke is composed of particles of nicotine and other chemicals that settle out of smoke and into surfaces and materials.
In addition to residual nicotine, thirdhand smoke contains cotinine and NNK.
Cotinine is a byproduct of nicotine that develops when it is metabolized. It is a known carcinogen.
NNK, another tobacco smoke byproduct, is thought to be a particularly potent carcinogen.
Evidence suggests that the chemical might corrupt DNA, encouraging the development of cancer.
Together these substances may also interact with other air pollutants to form new, additional carcinogens.
The latest study was published in the journal Environmental Science and Technology.
In one experiment, 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 accumulate 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 — which can be a critical factor in cancer development.
In the third experiment, three volunteers wore long-sleeved t-shirts and trousers that had been exposed to cigarette smoke for 30 days, at concentrations similar to those found in the home of a pack-a-day smoker.
The volunteers were not smokers and were not exposed to smoke at home or in work.
They wore the clothing for three hours and exercised enough to sweat for thirty minutes out of each of hour.
Urine specimens were collected prior to exposure, and at eight hours after the start of exposure
Each participant also completed the three-hour experiment in their normal clothes to establish a baseline.
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.
Researchers found levels of the chemical were 86 times higher in the samples taken after wearing the smoke-stained clothing.
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.’
Finally, researchers 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.’