This article is a commentary on the following study: Filleul L, Rondeau V, Cantagrel A, Dartigues JF, Tessier JF. Do subject characteristics modify the effects of particulate air pollution on daily mortality among the elderly? J Occup Environ Med. 2004 Nov;46(11):1115-22. The objective of this study is to examine the individual characteristics that may modify the relationship between exposure to urban air pollution and the risk of death. This article provides new insights into the individual factors that could modify the effects of air pollution on health in an elderly population. The statistical method used is rigorous and allows for a high level of confidence in the results. The analyses are based on a well-chosen population because it consists of older adults who have been prospectively followed for over 10 years. Furthermore, these results are of particular interest in terms of prevention. Of course, the observation of a three-day delay remains empirical, as no data currently exist to validate this notion. Certain factors modifying the effect of air pollution in this study appear consistent because they are associated with increased individual vulnerability, such as age or comorbidities (in this regard, asthma and diabetes are also associated with an increased risk, but the small sample sizes do not allow for reaching the threshold of statistical significance). Conversely, it is less straightforward to interpret the role of family status or home confinement. The explanation for lower levels of air pollution exposure among people in couples and those confined to their homes remains hypothetical and may vary with exposure to secondhand smoke. Similarly, the increased risk among individuals with a high level of education is surprising, whereas for the "occupational exposure" variable, blue-collar workers show an increased risk (possibly linked to higher occupational exposure to particulate matter). These results could be reinforced by future studies in other populations that might take into account exposure to fine particulate matter more precisely. In fact, current monitoring of particulate pollution is carried out through continuous measurement of PM10 and PM2.5. (Excerpts from the article).