Laws that have driven smoking out of offices, restaurants, public transport and other public spaces have reduced exposure to second-hand smoke, but a global study suggests the problem remains far from resolved. In 2023, about 2.71 billion people worldwide were still exposed to passive smoking, including 767 million children under 15. Research published in The Lancet Public Health estimates that second-hand smoke caused 1.6 million deaths that year and the loss of 44.8 million years of healthy life.
The proportion of people exposed has fallen substantially since 1990, declining from 43.6% to 33.9% in 2023, a relative reduction of 22.2%. Among children under 15, exposure fell from 51.7% to 37.9%. Yet the absolute number of people exposed increased from about 2.38 billion to 2.71 billion, reflecting the fact that reductions in prevalence have not been sufficient to offset global population growth.
The disparity is particularly pronounced in sub-Saharan Africa, where the number of people exposed has almost doubled since 1990. In North Africa and the Middle East, it increased by 72%.
“The proportion of the population exposed is falling, but it is doing so more slowly than the population is growing in those regions. Therefore, although prevalence is slowly declining, the number of people exposed is increasing,” said Luisa Sorio Flor, a researcher at the Institute for Health Metrics and Evaluation at the University of Washington and the study’s first author.
She added that the regions were also seeing a trend similar to active smoking, which is increasing slightly, particularly among women. That, she said, was also slowing the decline in passive exposure.
Latin America and the Caribbean recorded the largest fall in prevalence since 1990, at 38%, followed by high-income countries, with a 32% reduction. However, the region with the highest exposure in 2023 was Southeast and East Asia and Oceania, where 48.4% of the population was exposed.
The gender gap in that region was particularly wide. Exposure affected 59.5% of women compared with 37.4% of men. Globally, the corresponding figures were 37.3% and 30.6%.
In Spain, the study estimates that around 30% of the population was exposed in 2023, slightly below the global average. Exposure among children under 15, however, was estimated at about 51%, representing more than three million children. Around 8,000 deaths in Spain were attributed to second-hand smoke that year.
The researchers caution that the figures should not be interpreted as an exact death count. Mónica Pérez-Ríos, a researcher with the Tobacco Group of the Spanish Society of Epidemiology, said there were limited data on exposure to second-hand smoke, with data quality even weaker in developing countries.
That limitation, she said, did not diminish the significance of the study. The estimated global death toll ranges between 1.3 million and 2 million.
“It is an approximation of the impact, but it puts something fundamental on the table: tobacco smoke kills,” Pérez-Ríos said. “We are talking about a carcinogen that has no safe threshold of exposure. And, for many people, this exposure is not chosen.”
The study focused on people who did not smoke daily, avoiding the combination of risks from passive exposure and the substantially greater risks associated with active smoking. Researchers used 395 representative surveys from 119 countries to assess workplace exposure and 938 censuses and major surveys from 173 countries to estimate household exposure. A statistical model was then used to fill geographical and temporal gaps.
The study attributed 537,000 deaths in 2023 to ischaemic heart disease, making it the leading cause of death associated with second-hand smoke, followed by chronic obstructive pulmonary disease with 354,000 deaths, stroke with 278,000, lower respiratory infections with 185,000 and lung cancer with 161,000. Among children, lower respiratory infections accounted for the greatest burden.
Rodrigo Córdoba, a family doctor specialising in smoking, said that passive smokers accounting for almost one-fifth of the estimated eight million annual tobacco-related deaths worldwide “should attract a great deal of attention”.
He called for more smoke-free spaces and wider implementation of measures recommended by the World Health Organisation, including higher taxes, plain packaging and restrictions on advertising. He also argued that smoke-free regulations should cover vaping aerosols.
Spain’s Council of Ministers has this summer sent Congress a bill intended to expand smoke-free outdoor spaces. However, the proposed legislation does not address some measures that have shown the greatest impact in reducing smoking, including higher taxes and plain packaging.
