Breathing can kill—even without smoking.

3 juin 2025

#Nicotine #SecondhandSmoke #LungCancer #Prevention Lung cancer remains one of the leading causes of cancer-related deaths worldwide, accounting for over one in five cancer deaths. While active smoking is the dominant risk factor, an increasing proportion of cases are being observed among non-smokers, challenging the assumption that only tobacco users are at high risk. Among other suspected sources

#Nicotine #SecondhandSmoke #LungCancer #Prevention

Lung cancer remains one of the leading causes of cancer-related deaths worldwide, accounting for over one in five cancer deaths. While active smoking is the dominant risk factor, an increasing proportion of cases are being observed among non-smokers, challenging the assumption that only tobacco users are at high risk.

Among other suspected sources, secondhand smoke is an avoidable yet still underestimated risk factor. It exposes non-smokers to toxic and carcinogenic substances similar to those directly inhaled by smokers. Despite growing awareness and the adoption of anti-smoking laws in public spaces, exposure to secondhand smoke continues in private settings, where protective policies are limited or entirely absent.

In this context, primary prevention is a crucial public health strategy. However, available data are heterogeneous due to varying methodologies, reporting biases, and a lack of recent studies specifically focused on non-smokers.

This study aims to assess the link between secondhand smoke exposure and lung cancer risk among non-smokers, across different exposure contexts. It also seeks to provide a reliable risk estimate to support prevention efforts and guide public health policies.

Secondhand smoke: a real invisible danger?

Research shows that overall exposure to secondhand smoke is associated with an increased risk of lung cancer in non-smokers.

Domestic exposure—particularly in the presence of a smoking partner—is linked to a 41% higher risk, with a dose-dependent effect based on the duration and intensity of exposure.
Childhood exposure is also correlated with an increased risk, especially when both parents smoke. The risk is even more pronounced when the mother is a smoker, highlighting a specific vulnerability to early-life exposures. In the workplace, exposure to secondhand smoke is also significantly associated with lung cancer, particularly in enclosed environments such as restaurants, bars, or entertainment venues.

Sensitivity analysis confirmed the robustness of the estimates, and no publication bias was detected, reinforcing the statistical credibility of the results.

Read next: Pancreatic cancer and passive smoking: an unexpected link?

An underestimated threat that requires urgent attention

Lung cancer remains a highly lethal disease, with a significant share occurring in individuals who have never smoked. Among suspected environmental factors, secondhand smoke represents a silent but real threat to non-smokers. One of the major challenges lies in the underestimation of the risks linked to passive smoking. In this context, the study was initiated to quantify the impact of secondhand smoke exposure on lung cancer risk among non-smokers, depending on the place of exposure.

The results confirm that secondhand smoke is a significant and independent risk factor, with heightened risk in familial settings with prolonged exposure, particularly among children or spouses of smokers. These findings emphasize the urgency of making secondhand smoke a top priority for prevention, beyond public spaces alone.

However, several limitations restrict the scope of the results and justify the need for longitudinal studies, especially those incorporating exposure biomarkers. Exploring genetic interactions is another promising avenue, as is a detailed risk analysis by profession or socio-economic status. Such studies will be essential to refine early detection strategies and expand anti-smoking regulations to semi-private spaces, such as multi-unit housing, vehicles, or public parks—places where exposure remains frequent but insufficiently regulated.

Read next: Smoke less, think better?

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Scientific reference

Elkefi, S., et al. (2025). Second-Hand Smoke Exposure and Risk of Lung Cancer Among Nonsmokers in the United States: A Systematic Review and Meta-Analysis. International journal of environmental research and public health, 22(4), 595

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