More than 1.6 million people die each year from secondhand smoke
The share of the population exposed to tobacco smoke is falling, but more than 2.7 billion people worldwide are still affected
Laws that have driven smoking out of offices, restaurants, public transport and other public spaces over the past few decades have reduced exposure to secondhand smoke, but they are far from solving the problem. In 2023, an estimated 2.71 billion people worldwide were still exposed to secondhand smoke, including 767 million children under the age of 15. A study published in The Lancet Public Health estimates that the smoke inhaled by non-smokers caused 1.6 million deaths and the loss of 44.8 million healthy years of life globally that year.
The prevalence of secondhand smoke exposure fell from 43.6% in 1990 to 33.9% in 2023, a relative decline of 22.2%. Among children under 15, the reduction was somewhat greater, from 51.7% to 37.9%. However, the absolute number of people exposed rose from about 2.38 billion to 2.71 billion. The authors describe this as global stagnation: improvements have not been enough to offset population growth.
The imbalance is most pronounced in sub-Saharan Africa, where the number of people exposed has nearly doubled since 1990, and in North Africa and the Middle East, where it has increased by 72%.
“The proportion of the population exposed is falling, but more slowly than the population is growing in those regions,” says Luisa Sorio Flor, a researcher at the Institute for Health Metrics and Evaluation at the University of Washington and the study’s lead author, in a video call. “That is why, even though prevalence is declining slowly, the number of people exposed is increasing. We are also seeing a trend similar to active smoking there, which is rising slightly, especially among women, and that also slows the decline in secondhand exposure.”
At the other end of the spectrum, Latin America and the Caribbean recorded the largest drop in prevalence since 1990, at 38%, followed by high-income countries, at 32%. The region with the highest exposure in 2023 was Southeast and East Asia and Oceania, where 48.4% of the population was affected. The gender gap there is particularly striking: 59.5% of women were exposed, compared with 37.4% of men. Globally, the figures were 37.3% and 30.6%, respectively.
The study’s country-level breakdown places Spain at close to 30% exposure in 2023, somewhat below the global average. However, it estimates a much higher prevalence among children under 15, at around 51%, or more than three million children. Deaths attributable to secondhand smoke in Spain are estimated at roughly 8,000 that year.
The figures help illustrate the scale of the problem, but they should not be mistaken for a precise headcount. Mónica Pérez-Ríos, a researcher with the Tobacco Working Group of the Spanish Society of Epidemiology, notes that there is limited data available on exposure to secondhand smoke, and that the quality of the data is even poorer in developing countries.
That limitation, she stresses, does not diminish the value of the study. The central estimate falls within a range of between 1.3 million and 2 million deaths. “It’s an approximation of the impact, but it highlights something fundamental: tobacco smoke kills. We are talking about a carcinogen for which there is no safe level of exposure. And for many people, this exposure is not a matter of choice. That is why reports like this carry such a powerful public health message,” Pérez-Ríos adds.
The newly published analysis is limited to people who do not smoke daily, in order to avoid conflating the risks of secondhand smoke with the much greater risks associated with active smoking. Flor explains: “When there is a large disparity between male and female smoking rates, many women who do not smoke end up exposed because of household composition and the high likelihood of living with a smoker. That is what happens in much of Southeast Asia, East Asia and Oceania.”
To estimate workplace exposure, the researchers compiled 395 nationally representative surveys from 119 countries that asked respondents whether other people smoked in their workplace. For household exposure, they relied on 938 censuses and large-scale surveys from 173 countries, combining information on household composition with daily smoking prevalence to calculate the likelihood that a person lived with at least one smoker. A statistical model was then used to fill in geographic and temporal gaps.
Flor explains: “If five people live in a house and one smokes, the other four, provided they are not daily smokers themselves, are considered exposed. This is especially important for children: they do not smoke or work, so in our model their exposure comes from the household.”
Once prevalence had been estimated, the researchers reviewed the available evidence to determine how much secondhand smoke increases the risk of nine health conditions: ischemic heart disease, stroke, chronic obstructive pulmonary disease (COPD), lower respiratory infections, lung and breast cancer, type 2 diabetes, otitis media and asthma. They then applied those excess risks to mortality and disease data by location, age and sex. This does not mean, therefore, that secondhand smoke was listed as the cause of death on 1.6 million death certificates.
Ischemic heart disease was the leading cause of death attributable to secondhand smoke, accounting for 537,000 deaths in 2023. It was followed by COPD, 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 largest share of the health burden.
Rodrigo Córdoba, a family physician and tobacco-control specialist, says the fact that almost one-fifth of all tobacco-related deaths worldwide, estimated at around eight million a year, occur among passive smokers “should be a major wake-up call.”
“Smoke-free areas should be expanded, but the full set of measures recommended by the World Health Organization must also be implemented,” says Córdoba. “Raising taxes is what reduces consumption the most; progress must also be made on plain packaging and limiting advertising. Smoke-free rules should include vaping aerosols. We still have little long-term epidemiology on these products, but continuous inhalation of their emissions is not harmless.”
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