2.71 billion people breathed second-hand smoke in 2023, first global GBD estimate

The harm done by smoking to the person holding the cigarette is one of the best-documented facts in public health. The harm done to the people around them is harder to count, because the exposed person does nothing, reports nothing and often does not know the dose. A new analysis sets out to count it directly, and calls itself the first dedicated Global Burden of Disease study to quantify second-hand smoke (SHS) as a global risk factor across a broad range of outcomes [s1].

The scale it arrives at is large. In 2023, an estimated 2.71 billion people worldwide were exposed to second-hand smoke, including 767 million children aged 0–14 years [s1]. For context, the World Health Organization's tobacco fact sheet records that tobacco kills more than 7 million people each year, including over 1.6 million non-smokers exposed to second-hand smoke, and that around 80% of the world's 1.2 billion tobacco users live in low- and middle-income countries [s2].

Falling rates, flat numbers

The study's central tension is between two kinds of progress. Using the GBD 2023 comparative risk assessment framework, the authors estimated exposure and attributable burden across 204 countries from 1990 to 2023 [s1]. Age-standardised prevalence fell 22.2% since 1990 [s1] — a real decline that tracks decades of indoor-smoking bans and falling smoking rates.

But a falling rate applied to a growing, ageing population does not necessarily shrink the number of people affected. The authors are explicit that the progress has not been sufficient to reduce the absolute number of exposed individuals, which has remained stable globally and has risen sharply in sub-Saharan Africa, up 98.5%, and in North Africa and the Middle East, up 72.1% [s1]. Those two regions are where tobacco control is weakest and the population youngest, and they are the places where the relative-versus-absolute gap matters most.

Who is exposed

Exposure is not evenly distributed, and the pattern is the opposite of what a naive model of smoking would predict. Age-standardised prevalence was highest in southeast Asia, east Asia, and Oceania, at 48.4% [s1]. And in some countries, female individuals experienced nearly 1.8 times the exposure prevalence of male individuals [s1] — a gap that reflects who smokes in public and who is exposed at home, rather than who chooses to light up.

That domestic geography is the uncomfortable core of the paper. Public-place bans, which most countries now have in some form, do not reach the home. The people with the least control over their own exposure — women in households where men smoke, and children of any household member who does — are the ones the headline prevalence figure is built on.

The disease it causes

The burden estimate is where the abstraction becomes mortality. In 2023, SHS exposure accounted for 1.66 million deaths and 44.8 million disability-adjusted life-years (DALYs) globally [s1]. The analysis assessed nine health outcomes, now including asthma, using the Burden of Proof methodology [s1].

The cause breakdown matters for policy. Ischaemic heart disease was the leading contributor to SHS-attributable DALYs overall, at 12.0 million, while lower respiratory infections predominated among children, at 5.16 million [s1]. Second-hand smoke, in other words, is primarily a cardiovascular problem in adults and a respiratory one in children — the same split the WHO fact sheet describes when it lists heart disease, stroke and lung disease among tobacco's harms [s2].

That the single largest slice is heart disease rather than lung cancer is the finding most likely to be misremembered. The cultural association between passive smoking and cancer is strong, but the arithmetic of the global burden runs through the coronary arteries.

What the authors ask for

The paper's interpretation is a call for enforcement rather than new science. The authors argue that persistent geographical disparities and the growing absolute numbers of exposed individuals underscore the urgent need for accelerated implementation and enforcement of comprehensive tobacco control measures, particularly to protect women and children in both public and domestic environments [s1].

The WHO's own tobacco-control package points the same way, listing the enforcement of bans on tobacco advertising, promotion and sponsorship, and higher tobacco taxes, among its core demand-reduction measures [s2]. The second-hand-smoke numbers are, in effect, a measure of how much of that package has reached the places smoke actually travels — across a room, not across a border. The study was funded by Bloomberg Philanthropies and the Gates Foundation [s1].

What to watch

The measurable question the next GBD round will answer is whether the absolute number of exposed people finally turns down, or whether the regional increases in sub-Saharan Africa and North Africa and the Middle East [s1] keep the global count flat. A falling rate with a flat count would mean the policies are working on paper while the exposed population keeps growing — the same pattern the injury and non-communicable-disease literatures keep rediscovering in a world that is getting both older and more crowded.

Sources

• Global, regional, and national prevalence of second-hand smoke and attributable disease burden in 204 countries and territories, 1990–2023: a systematic analysis for the Global Burden of Disease Study 2023, The Lancet Public Health, 7 September 2026
• Tobacco (fact sheet), World Health Organization