This article is published in partnership with Dialogues économiques, produced by Aix-Marseille School of Economics (AMSE).

According to the French public health agency Santé Publique France, tobacco killed around 68,000 people in France in 2024, or some 186 deaths per day. Worldwide, it is responsible for more than 8 million fatalities each year, according to the World Health Organization. Despite the scientific consensus on its harmful effects, and decades of prevention measures such as awareness campaigns, plain packaging, graphic warning labels, and price increases, nearly a quarter of French adults still smoke. Why is it so difficult to change behaviours?

Beyond public health messaging, personal experience – such as a loved one falling ill or a parent diagnosed with a smoking-related cancer – might be expected to act as a wake-up call and permanently change habits. But is that really the case? Researchers Sylvie Blasco, Eva Moreno Galbis, and Jeremy Tanguy examine the impact of a “family shock”, such as a relative’s diagnosis, on behaviour. Their study1 offers important insights for public health policy.

The researchers drew on data from the Constances cohort2, a large-scale public health programme tracking more than 220,000 adults in France over several years. Participants report their lifestyle habits annually, including tobacco use, along with medical check-ups and family health histories. This allows researchers to reconstruct individual smoking trajectories over time.

Seeing a parent smoke and be a victim of tobacco does not necessarily deter a child from becoming addict to cigarettes.

Seeing a parent smoke and be a victim of tobacco does not necessarily deter a child from becoming addict to cigarettes.

ClarkandCompany / iStockphoto.com

ClarkandCompany / iStockphoto.com

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Mixed findings in earlier research

The study fits into a broader body of work in health economics on risk behaviours following a parent’s diagnosis. Earlier research3 has evidenced that health shocks can shift individual preferences. For example, the American economists Michael Darden and Donna B. Gilleskie observed4 a slight decline in smoking, mainly among daughters, after a father experienced a cardiovascular event. Other research on the intergenerational transmission of behaviour points to a sort of continuity and generally concludes that the effects are weak or even non-existent.

The richness of the Constances cohort enabled the researchers to determine whether a diagnosis of lung or another smoking-related cancer in parents affects their children’s smoking habits. They also explored how the impact varies depending on the child’s age at the time of the diagnosis.

To do so, they used tools from health economics and econometrics5 to isolate the effect of a specific event on behaviour over the long term. The aim was to determine whether an “information shock”, in this case a parent’s diagnosis of a tobacco-related cancer, alters individual decision-making independently of other factors already at play, such as family transmission or risk perception. This approach helps limit confounding biases and comes as close as possible to identifying a causal relationship.

Adolescence, a turning point

The findings may come as a surprise. Counterintuitively, in most cases, seeing a parent develop cancer does not trigger any significant change in the behaviour of their children once they reach adulthood. The effects are limited and rarely statistically significant. The shock appears too indirect to disrupt deeply ingrained habits.

There is one exception though. When the diagnosis occurs during adolescence, between the ages of 15 and 18, the likelihood of smoking decreases. The authors show that this is a critical period when many youngsters decide whether to start smoking. When a parent’s diagnosis coincides with this window, the information shock is more likely to influence behaviour.

Average age of becoming a smoker.

Average age of becoming a smoker.

J. Tanguy, S. Blasco, E. Moreno-Galbis, hal-04609760 CC BY 4.0

J. Tanguy, S. Blasco, E. Moreno-Galbis, hal-04609760 CC BY 4.0

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The need for personalised information

How can the gap between intuition and observed outcomes be explained? Behavioural economics offers several explanations. First, risk often remains abstract. Even when confronted with a loved one’s illness, many people still believe they themselves will never be affected.

The economist Christian Bünnings6, who has studied decision-making under known risks, shows that individuals need information that feels personal and adapted in order to truly adjust their perception of danger. Risk assessment is gradual and often incomplete7. Knowing the hazards is not enough. People must also feel personally concerned8.

The study directly challenges current prevention strategies. Many public health campaigns are based on the idea that exposing people to consequences is sufficient to change behaviour. These findings point to the limits of that approach, and to the need to rethink levers for action, especially among younger populations. Prevention is most effective before habits become firmly established.