Susceptibility and Vulnerability of Children to Wildfire Smoke Exposure: Important Considerations and Remaining Knowledge Gaps

As the climate continues to change, wildfire smoke has emerged as an essential threat, impacting populations well beyond the immediate vicinity of fire events. Wildfires are becoming more frequent, intense, and widespread, leading to increased exposure to smoke-related pollutants [1]. The composition of wildfire smoke is notably complex, containing a mixture of pollutants that is potentially more harmful than typical ambient air pollution [2]. While research has firmly established the respiratory impacts of wildfire smoke exposure, significant knowledge gaps persist, including understanding the health effects of extended exposure periods and the specific implications for vulnerable populations. In this issue of Paediatric and Perinatal Epidemiology, Syed and Basu [3] synthesised existing research on the effects of wildfire smoke exposure on a particularly vulnerable population: children. We applaud Syed and Basu for highlighting this critical and understudied topic. In this commentary, we aim to emphasize the pressing need for further studies and interventions in this rapidly evolving field. Children represent a particularly vulnerable population when it comes to wildfire smoke exposure, owing to a combination of behavioural and physiological factors. Their developing respiratory systems are more susceptible to the detrimental effects of both ambient and wildfire-related air pollutants. Physiologically, children have a higher breathing rate relative to their body size, which increases their exposure to airborne contaminants. Their smaller airways are more prone to obstruction when irritated by smoke particles [4]. Behaviourally, children tend to be more physically active and spend more time outdoors compared to adults, potentially increasing their exposure to wildfire smoke pollutants. Furthermore, the ongoing development of children's immune systems in the years following birth may contribute to their heightened sensitivity to the harmful effects of smoke inhalation [5]. These combined factors underscore the critical importance of protecting children during wildfire events and highlight the need for targeted research and interventions focused on this vulnerable group. Syed and Basu [3] reported that associations across studies tended to be stronger among children under five, who had higher body mass index or who were asthmatic. They also briefly mentioned social and economic marginalisation as a source of inequities in the effects of wildfire smoke: children with disabilities, from disadvantaged neighbourhoods, from racially minoritised groups, and low-income countries tended to bear the burden of wildfire smoke exposure's effects on health. We want to expand on this point, as it is crucial for developing interventions to protect communities from the growing threats of wildfire smoke. First, marginalised communities are disproportionately exposed to wildfire smoke: an analysis of national data from 2011 to 2021 showed notable increases in heavy smoke days in communities with a high proportion of racially minoritised residents, residents with low English proficiency, residents with low educational attainment and crowded housing conditions [6]. These communities are frequently situated in regions with higher ambient pollution levels, further compounding their susceptibility to the effects of wildfire smoke inhalation [7]. Second, marginalised communities have fewer resources and capacity to reduce personal exposure during wildfire events, including limited access to air conditioning, lack of adequate indoor air filtration systems, poor quality or inadequate housing, and financial constraints preventing evacuation. Third, socially and economically marginalised communities are inequitably exposed to other social and environmental stressors that could exacerbate the effects of wildfire smoke exposure and experience a higher prevalence of pre-existing health conditions that could make the health consequences of exposure more severe [8]. When considering children, a population Syed and Basu accurately and succinctly describe as ‘… more behaviourally exposed and more physiologically vulnerable’, issues of environmental justice are even more crucial. Targeted interventions and policies that are developed with marginalised communities—not just on their behalf—are essential to protecting children from the disproportionate impacts of wildfire smoke exposure. Syed and Basu identified other gaps in the existing literature, including the effects of wildfire smoke on non-respiratory outcomes, identification of acute versus chronic health outcomes, identification of critical windows of susceptibility, and differential effects by age group (i.e., < 1, 1–4, 5–12 and 13–18 years). We wish to draw attention to an additional research gap: considering concurrent and cascading climate-related exposures. Climate hazards that occur together (concurrent) or one after the other (cascading), including drought, extreme heat, and wildfires, are becoming increasingly frequent and intense. These interconnected hazards often amplify each other, creating complex and compounding risks for public health. Researchers have proposed that the combined, synergistic effects of multiple chemical and non-chemical climate-related exposures may enhance their individual impacts, potentially resulting in overall effects that exceed the sum of their separate influences [9]. Although few studies have comprehensively examined these combined factors, recent investigations have revealed the frequent co-occurrence of extreme temperatures and wildfire smoke exposures and a positive synergistic impact of these compound exposures [10]. The limited focus on children in existing studies further compounds the need for more research on combined exposures. Other climate hazards, notably extreme heat, have been associated with paediatric health outcomes, but there has been virtually no assessment of concurrent or cascading climate hazards on children's health. Given expert predictions of an increase in concurrent and cascading events in the coming decades, [11] this knowledge gap is particularly concerning. Understanding the intricate interplay between these exposures and their specific impacts on vulnerable populations, especially children, becomes increasingly crucial for developing effective public health strategies and interventions as climate change continues to alter environmental patterns. Reproductive justice is ‘the human right to maintain personal bodily autonomy, have children, not have children, and parent the children we have in safe and sustainable communities’ [https://www.sistersong.net/reproductive-justice/]. Given the convergence of children's heightened vulnerability, the stark inequity in exposure and health effects across communities, and the growing threat of concurrent climate events, the wildfire crisis is a direct threat to reproductive justice. More research is crucial to understand the full scope of impacts and develop effective strategies to safeguard children from increasingly prevalent and intense wildfires as the climate changes. Indeed, gaps in the scientific literature need to be addressed, but multi-disciplinary action is necessary to move beyond the documentation of adverse effects. Syed and Basu have outlined several public health strategies for protecting children from wildfire smoke, including roles for paediatricians and other clinicians, schools and families. We strongly encourage collaboration between academic researchers (e.g., epidemiologists, environmental health scientists and experts in implementation science), public health practitioners, clinicians and—importantly—trusted community partners, to develop effective interventions and policies to protect children from the growing threat of wildfires. Jennifer D. Stowell: conceptualisation, manuscript writing, editing. Amelia K. Wesselink: conceptualisation, manuscript writing, editing. The authors have nothing to report. The authors declare no conflicts of interest. The authors have nothing to report.