Almost two million people worldwide could be dying every year as a result of second-hand smoke, a major study has found.
Also known as passive smoking, it occurs when someone breathes in smoke from another person’s cigarette, pipe or cigar.
And even small amounts can be harmful – raising the risk of heart disease, stroke, lung conditions and cancer.
In the UK alone, researchers estimated that second-hand smoke was responsible for 6,100 deaths in 2023 – making it deadlier than diseases such as bladder cancer.
That is a dramatic fall from 14,900 deaths in 1990, but scientists behind the new study, published in The Lancet Public Health, warn that passive smoking still ‘remains a substantial driver of global health loss’.
The findings reveal just how deadly exposure to other people’s smoke can be – and which diseases are responsible for the greatest toll.
Researchers led by the University of Washington say their study is the first to assess second-hand smoke as a ‘global risk factor’.
Researchers did not directly count deaths caused by passive smoking.
Almost two million people worldwide could be dying every year as a result of second-hand smoke, a major study has found
Instead, they first estimated how many non-smokers were exposed to other people’s smoke at home or work.
They then drew on previous studies that have established how much passive smoking raises the risk of nine diseases, including heart disease, stroke and lung cancer.
By combining these known risks with figures showing how many people were exposed and how many died from each disease, they could estimate how many of those deaths would not have occurred without passive smoking.
The estimates, covering 204 countries, found that 2.71 billion people were exposed to second-hand smoke in 2023 – including 767 million children aged 14 or younger.
Overall, researchers estimated that second-hand smoke was responsible for around 1.7 million deaths worldwide that year.
Despite the proportion of people exposed falling by around 22 per cent since 1990, population growth meant the total number remained roughly the same.
Heart disease was by far the biggest killer, accounting for an estimated 537,000 deaths linked to second-hand smoke in 2023.
This was followed by chronic obstructive pulmonary disease (COPD), with 354,000 deaths, stroke with 278,000, lower respiratory infections with 185,000 and lung, bronchial and tracheal cancer with 161,000.
The greatest toll was seen in South East Asia, East Asia and Oceania, where around 689,000 deaths were linked to second-hand smoke, followed by South Asia with around 428,000.
Researchers said second-hand smoke exposure remains particularly high across much of Asia, reflecting persistently high smoking rates in many countries. China, India and Indonesia alone accounted for almost half of all people exposed worldwide.
Britain, however, has seen a huge improvement over the past three decades.
Around 30 per cent of British adults smoked cigarettes in 1990, compared with roughly ten per cent today, separate figures show.
Over the same period, the number estimated to be exposed to second-hand smoke fell from 19.8 million to 15.5 million.
Deaths linked to passive smoking more than halved, from around 14,900 in 1990 to 6,100 in 2023.
But the health burden remains substantial.
Second-hand smoke was linked to around 385,000 years of healthy life lost through illness, disability or premature death in Britain in 1990. By 2023, the figure was still around 171,600.
The researchers called for tougher measures around the world, including higher tobacco taxes, advertising bans, plain packaging and greater access to stop-smoking programmes.
Many of these measures are already in place in Britain, where cigarette packaging is standardised and tobacco advertising banned.
And the true toll of passive smoking could be even higher.
The researchers were only able to track exposure at home and at work, meaning exposure elsewhere – including in cars and hospitality venues – was not captured.
They were also unable to measure how long individuals were exposed.
However, experts have long warned that even brief exposure can be harmful.
The NHS says: ‘When friends and family breathe in your secondhand smoke – what we call passive smoking – it is not just unpleasant for them, it can damage their health too.’
It also warns that exposure during pregnancy is linked to premature birth, low birthweight and sudden infant death syndrome.
Around 4.9 million British adults smoke cigarettes, while the number who vape now exceeds the number of smokers by around 500,000.
Unlike cigarettes, e-cigarettes do not produce tobacco smoke, meaning the risks associated with passive smoking do not apply in the same way to vaping, according to the NHS.
