Why are children so vulnerable to air pollution?
2.1 Early vulnerability, lifelong risks
Many health effects of exposure to air pollution early in life manifest only later, as today’s children become tomorrow’s adolescents and adults. Children’s longer life expectancy gives the mechanisms of latent disease more time to emerge and damage health (49). It is therefore essential that health professionals and policy-makers adopt a life-course approach to addressing the threats of air pollution to children to account for the full spectrum of health risks across the lifespan (Fig. 3).
The risks start during pregnancy, when maternal exposure to air pollution can impair fetal growth. Exposure to ambient air pollution during this time increases infant mortality, affects development of the brain and leads to increased risks of respiratory illness (see section 3). Exposure of pregnant women can also lead to other adverse birth outcomes, such as preterm birth and low birth weight (50).
A child’s earliest years are critically important for cognitive and physiological development. During this time, their lungs and organs develop rapidly. Their likelihood of contracting NCDs such as COPD, heart disease and stroke in adulthood can therefore be influenced by exposure to air pollution (51). They are also at higher risk of metabolic disorders such as diabetes (52).
As a child grows, exposure to air pollution can contribute to the emergence of chronic respiratory diseases such as asthma and childhood cancers. These diseases can reduce children’s ability to learn, attend school, engage in recreational activities and develop to their full potential. Other health burdens such as impaired lung function and cognitive effects can occur later in childhood or in adulthood. Some adverse impacts can last throughout life (53).
2.2 Physiological and other factors
Several physiological factors make children more susceptible to air pollution (54). Children have immature immune, respiratory and central nervous systems and are highly sensitive to environmental stimuli, including air pollution (50). Their airways and blood vessels are narrower. Their metabolic processes are still maturing. These anatomical, physiological and development factors interact to place children at greater risk of adverse health effects from air pollution (Fig. 4)
2.3 Child mortality and burden of disease
The global under-5 mortality rate from all causes has decreased by more than 50% since 2000. Nevertheless, in 2023, 6.9 million infants, children, adolescents and youth died worldwide. Children under 5 accounted for 4.8 million of those deaths, 2.3 million of which occurred in the neonatal period (0–27 days) and 2.5 million were among children aged 1–59 months (70) (Fig. 5).
Acute lower respiratory infection (ALRI), a category of disease associated with exposure to air pollutants, is the second-leading cause of death in children under 5 worldwide, after prematurity (other important causes of death are birth asphyxia, birth trauma, malaria and diarrhoea) (71). The trend in the number of deaths from ALRI since 2000 is clearly decreasing, but they occur disproportionately in LMIC and in fragile and conflict-affected areas (70,72). Many deaths from ALRI, which represented 14% of all deaths in children under 5 in 2021, could be prevented by addressing indoor and outdoor air quality (65).
2.4 Universal threat but unequal burdens
2.4.1 Ambient air pollution
In 2023, more than 900 million children (almost 40% of the 2.4 billion children) exposed to unsafe levels of air pollution fight for breath against air loaded with PM2.5 at an annual average of > 35 µg/m³, seven times higher than the WHO recommended levels (Fig. 7) (75). Of these children, the 98.7% who live in LMIC have a higher incidence and greater severity of a wide array of acute and chronic health problems with potentially lifelong consequences. This burden falls on a small number of countries: 91% of children
2.4.2 Household air pollution
In 2023, some 820 million children in LMIC are exposed to household air pollution because of lack of access to clean cooking fuels and technologies. This risk factor affects mainly poor households and communities and is almost inexistent in high income countries (Figs 9 and 10).
2.4.3 Mortality of children under 5 attributable to ALRI
While the overall trends in age-standardized mortality rates attributable to exposure to air pollution from PM (SDG indicator 3.9.1) show a