'Thirdhand' smoke a health risk in cinemas, say researchers

The lights dim, the trailers roll and the mutter of voices dwindles to a hush. But alongside the smell of popcorn, another scent pervades the cinema: the waft of stale cigarette smoke.

Now scientists say they have measured levels of such “thirdhand” smoke, suggesting it is carried on the bodies and clothing of moviegoers and could be a prominent, and lingering, source of hazardous chemicals.

“This represents significant but poorly understood health risks to non-smokers and a source of reactive chemicals indoors,” said Dr Drew Gentner, co-author of the research from Yale University, noting that previous studies suggest thirdhand smoke may account for between 5% and 60% of the combined disease burden from cigarette smoke in non-smokers.

Writing in the journal Science Advances, researchers report how they tracked traces of cigarette smoke in a German cinema – a venue where smoking is not permitted. The cinema was 1,300 sq metres in size, and supplied with fresh, filtered air from outside.

The team sampled the exhaust air duct of the cinema for four days and detected 35 volatile substances that are found in tobacco smoke, including formaldehyde and the carcinogenic chemical benzene.

Concentrations of such substances showed a spike when customers entered the screening. Less pronounced spikes were seen for earlier showtimes, while levels of the substances were lower for family films than for “R-rated” action films aimed at older cinemagoers, despite the latter having smaller audiences.

“In the R-rated films, especially the ones that are occurring later in the evening, it appears there’s a greater propensity of people attending those movies to have smoked, or perhaps to have smoked more frequently or more cigarettes, and so they are off-gassing more,” said Gentner.

Analysis of particular substances revealed that, in the case of the action films, the thirdhand smoke was relatively “fresh”, while its presence in family films was older – possibly down to substances lingering from previous screenings.

The team found signs that substances from thirdhand smoke build up over time.

“That’s because the chemicals don’t remain entirely in the air, but are also absorbed on to various surfaces and furnishings from which they re-enter the air over time,” said Gentner.

The researchers also collected samples of fine, airborne particles from the cinema and analysed the substances stuck to them. Among those detected was nicotine.

The team said the upshot was that those going to R-rated films were exposed, on average, to the equivalent of secondhand smoke from between one and 10 cigarettes, depending on the substance in question.

The study involved audiences of different sizes, and it was not clear which moviegoers had previously been smoking or exposed to smoke. The team did not look at how exposure to thirdhand smoke varied with proximity to a source.

“The people in the room will all be exposed to the same number of secondhand smoke equivalents in terms of emissions, but the total mass of the compounds they inhale will change with their proximity to the source,” said Gentner.

The team say the study offers a real-life example of exposure, adding that other spaces, which may be smaller with poorer ventilation – such as bars, offices and underground trains – could have much higher levels of thirdhand smoke.

Prof John Britton, director of the UK Centre for Tobacco and Alcohol Studies and consultant in respiratory medicine at Nottingham University, said the results were not surprising. “This study confirms what anyone with a sense of smell has already worked out: that smokers carry and emit tobacco smoke components into the atmosphere even when not smoking,” he said.

“In reality the exposure sustained by others in such circumstances is low, and any health risk likely to be likewise,” he added, although he called for more research into potential impacts.

Others said it was not clear whether the levels of thirdhand smoke detected were high enough to cause health problems.

“It is a long road … to showing that there is anything that non-smokers should be concerned about,” said Martin Jarvis, emeritus professor of health psychology at University College London, who was not involved in the research.

Prof Jacqui Hamilton, an expert in aerosol chemistry and air quality from York University noted that, while the detected emissions included hazardous chemicals such as benzene and formaldehyde, some of the most toxic compounds within thirdhand smoke – tobacco-specific nitrosamines – were not detected, although it was not clear why.

“Only very small levels of exposure to these compounds have the potential to increase cancer risk and future studies could investigate this to understand the full impact of tobacco-related emissions on non-smokers,” Hamilton said.