UNICEF - Environmental determinants of respiratory disease in children

Environmental determinants of respiratory disease in children Executive summary © UNICEF/UNI827582/Urdaneta Respiratory diseases are a leading cause of illness and death among children around the world, especially in lowand middle-income countries (LMICs). Nearly 500,000 children under 5 years of age die every year from pneumonia, mostly in LMICs. Air pollution is a major risk factor for childhood respiratory diseases. Common sources of air pollution are household fuel burning (e.g., for cookstoves), transport emissions, waste burning, industrial emissions, wildfires and dust storms/sandstorms. Second-hand tobacco smoke is another source of dangerous air pollution for children. Many sources of air pollution that are harmful to health also release greenhouse gases that cause global climate change; therefore, many policy solutions for cleaner air also have social and environmental cobenefits. Children deserve to breathe clean air where they live, play and learn. To protect children’s lungs, comprehensive policies that reconsider children’s unique vulnerabilities are urgently needed. Priority areas for reducing childhood respiratory diseases include reducing smoking and exposure to second-hand smoke; ensuring universal access to clean household fuel and cookstoves; enforcing air quality standards; investing in green spaces and improved land/water management systems; developing preparedness systems for communities, schools and childcare centres; and enhancing community engagement efforts. © UNICEF/UN073954/Clarke for UNOCHA 1Introduction Respiratory diseases are a significant cause of illness and death among children around the world, especially in lowand middle-income countries (LMICs). Breathing in polluted air is a major risk factor for childhood respiratory diseases. Air pollution damages the lungs and makes children more vulnerable to potentially life-threatening respiratory infections like pneumonia. As well as causing respiratory infections, exposure to air pollution can affect lung growth and function and increase the risk of asthma, allergic airway diseases and middle-ear infections.

damages the lungs and makes children more vulnerable to potentially life-threatening respiratory infections like pneumonia. As well as causing respiratory infections, exposure to air pollution can affect lung growth and function and increase the risk of asthma, allergic airway diseases and middle-ear infections. Henri is a three-year-old boy living in a small community on the outskirts of a city in Senegal. Although he was born preterm and was small for his gestational age, he is now an active child and enjoys playing with his siblings. He also enjoys helping his mum to prepare meals over their open-fire cookstove that burns wood and crop waste. One day, Henri woke up with a fever and cough. He tried to join his siblings in play; however , he felt tired and was not able to run around like he usually does. As the day progressed, his mother noticed that he was breathing more rapidly. By evening, she noticed that the muscles and skin between his ribs pulled inward when he breathed. Henri was not able to sleep well, and by morning he was struggling to breathe and his fever was even higher than the day before. His family rushed him to a community clinic, which had recently received both oxygen systems and antibiotics through the Scaling Pneumonia Response Innovations (SPRINT) programme established by UNICEF. The nurse placed an oxygen monitor on his finger and found that his oxygen levels were low. When examining his lungs, she noted that he had congested airways and poor airflow. He was diagnosed with severe pneumonia and placed on oxygen therapy. After receiving a dose of antibiotics, he was sent to a hospital in the nearest city for more treatment. Henri represents one of the millions of children who suffer from severe pneumonia every year . Fortunately for Henri, he recovered after four days in the hospital. Within a week of discharge, he was able to rejoin his siblings in their favourite games. Unfortunately, however , about 500,000 children under 5 years of age die every year from pneumonia (Wang et al., 2025). Breathing polluted air is a leading risk factor for pneumonia among children

able to rejoin his siblings in their favourite games. Unfortunately, however , about 500,000 children under 5 years of age die every year from pneumonia (Wang et al., 2025). Breathing polluted air is a leading risk factor for pneumonia among children in lowand middle-income countries. Furthermore, air pollution has been identified as the second highest risk factor for death among children under 5 years (after malnutrition) (Health Effects Institute, 2024). Box 1. Addressing severe pneumonia in a young child © UNICEF/UNI556817/Nimani 2A child’s respiratory system is uniquely vulnerable to pollution Children are not simply ‘little adults’ – they have unique physiological and behavioural vulnerabilities that put them at more risk than adults of environmentrelated illness. This is especially true for the respiratory system – organs (lungs) and structures (upper and lower airways) that allow you to breathe in oxygen and exhale carbon dioxide. From the in utero period to adolescence, exposure to air pollution can lead to respiratory diseases and decreased lung function because the lungs are still developing. Lungs start to develop early during the in utero period (at around four to seven weeks of gestation). By nine months of gestation, the alveoli (air-exchange area) are developing (Aithal et al., 2023). After birth, the lungs (including the alveoli) are not yet fully developed, and they continue to mature until young adulthood. Pregnant women breathe in more air per minute than non-pregnant women, and air pollutants that are inhaled can be absorbed into the bloodstream. Some of these pollutants can then cross the placenta and affect the growth and development of the fetus. Prenatal exposure to air pollution can contribute to preterm birth and low birth weight, both of which put children at increased risk of respiratory disease as they get older . Furthermore, prenatal exposure to air pollution can impact a child’s lung health even after they are born – putting them at increased risk of

Prenatal exposure to air pollution can contribute to preterm birth and low birth weight, both of which put children at increased risk of respiratory disease as they get older . Furthermore, prenatal exposure to air pollution can impact a child’s lung health even after they are born – putting them at increased risk of pneumonia in early life and of developing asthma and allergic diseases during childhood. Infants and children breathe more air per kilogram of body weight than adults. When a child’s small airways are exposed to certain air pollutants, inflammation (swelling) can occur that leads to more blockage and resistance to airflow than that observed in adult airways. Several respiratory problems are linked to childhood air pollution exposure, including pneumonia, asthma, upper respiratory tract infections and allergic disease. Because lung function development continues until young adulthood, adolescents are also susceptible to air pollution. They may spend more time outdoors than adults and participate in physical activity near areas of pollution. Some adolescents may have trouble managing respiratory symptoms as they gain autonomy (e.g., carrying and using asthma inhalers appropriately) (UNICEF, 2025). Air pollution is a leading risk factor for respiratory disease in children Air pollution, which can be generated indoors and outdoors, is a leading environmental factor contributing to respiratory disease and death worldwide. Globally, approximately 2 billion people still use open fires or inefficient cookstoves that burn solid fuels inside their homes, releasing dangerous amounts of pollutants. Ambient (outdoor) air pollution is generated from many sources that include vehicles, industrial facilities and waste burning, and the resulting pollutants can be released locally within a community or elsewhere and transported great distances. Although levels can vary dramatically from place to place and over time, 99 per cent of the global population in 2019 lived in areas where the World Health Organization (WHO) ambient air quality guidelines (AQGs) were not being met (World Health Organization, 2024b). While deaths related to air pollution among children

from place to place and over time, 99 per cent of the global population in 2019 lived in areas where the World Health Organization (WHO) ambient air quality guidelines (AQGs) were not being met (World Health Organization, 2024b). While deaths related to air pollution among children under 5 years old have decreased by 53 per cent since 2000, more work is needed to protect children’s health, especially the health of those living in LMICs. Air pollution is still linked to more than 40 per cent of all deaths from lower respiratory tract infections in young children in many African and Asian countries (Health Effects Institute, 2024). © UNICEF/UNI520717/Khatri Around the world, more than 2,000 young children under 5 years of age die each day from air pollution-related causes (notably pneumonia). 3Diseases of the respiratory system (airways and lungs) in children are a significant cause of death around the world and contribute to the global burden of disease (Table 1). Lower respiratory tract infections (e.g., pneumonia) and asthma are common respiratory diseases that impact children’s health, development and quality of life. These respiratory diseases put economic and social burdens on children and their families (e.g., in relation to health-care costs, school absenteeism, work absenteeism for caregivers, stress). Other common respiratory conditions are impaired lung growth and function, upper respiratory tract infections and ear infections. Stark disparities are seen with respiratory diseases, with morbidity and mortality related to these diseases being higher among children living in LMICs than elsewhere. This is related to the inadequate health-care infrastructure, poverty and environmental pollution in these countries. Burden of childhood respiratory disease Respiratory disease Description Annual global burden of disease (2023) Environmental risk factors Lower respiratory tract infections • Infection with virus, bacteria or fungus that causes inflammation in lungs (e.g., pneumonia) • 242 million incident cases

Burden of childhood respiratory disease Respiratory disease Description Annual global burden of disease (2023) Environmental risk factors Lower respiratory tract infections • Infection with virus, bacteria or fungus that causes inflammation in lungs (e.g., pneumonia) • 242 million incident cases • 98.7 million DALYs • 13% of deaths for children under 5 years • Household air pollution • No access to handwashing • Ambient air pollution (PM) • Second-hand smoke • Smoking Tuberculosis • Mycobacterium infection that typically impacts lungs but can spread to other organs • 8.3 million incident cases • 43.6 million DALYs • Household air pollution • No access to handwashing • Ambient air pollution (PM) • Second-hand smoke • Smoking Asthma • Most common chronic lung disease in children • Airway inflammation, mucus and reversible constriction • Prevalence: 362.6 million • 25.8 million DALYs • Ambient air pollution (NO2, PM, O3) • Smoking • Second-hand smoke • Occupation (e.g., contact with chemicals) • Allergens Upper respiratory tract infections • Issues such as cough, rhinitis, sinusitis, pharyngitis • 13.2 billion incident cases • 6.2 million DALYs • Second-hand smoke • Ambient air pollution (PM) Otitis media • Infection of middle ear • Can impact hearing • 394 million incident cases • 2.5 million DALYs • Second-hand smoke Table 1. Global burden of disease and environmental risk factors for common respiratory diseases DALY, disability-adjusted life year; NO 2, nitrogen dioxide; O3, ozone; PM, particulate matter . Source of 2023 annual burden of disease data: Institute for Health Metrics and Evaluation (2023). GBD results [Data set]. https://vizhub. healthdata.org/gbd-results/ . (accessed 8 April, 2026). 4Lower respiratory tract infections Lower respiratory tract infections, including

Source of 2023 annual burden of disease data: Institute for Health Metrics and Evaluation (2023). GBD results [Data set]. https://vizhub. healthdata.org/gbd-results/ . (accessed 8 April, 2026). 4Lower respiratory tract infections Lower respiratory tract infections, including pneumonia, are a leading cause of illness and death in young children. Pneumonia is an infection of the lung tissue caused by a bacteria, virus or fungus that leads to inflammation in the alveoli (air-exchange area) and makes it hard to breathe. Exposure to air pollution, especially fine particulate matter (also known as PM2.5), damages the lungs of children because it can travel to the deepest parts of the lung. This causes inflammation in the lung and compromises the immune system response in the airways, which makes a child more susceptible to severe infections (e.g., pneumonia) (Monoson et al., 2023). As demonstrated by the case study of three-year-old Henri (Box 1), severe pneumonia can make it difficult for children to breathe and get enough oxygen into their body. In 2021, 13 per cent of deaths in children under 5 years old were caused by lower respiratory tract infections (United Nations Inter-agency Group for Child Mortality Estimation, 2026). Exposure to household air pollution nearly doubles the risk of a child developing a lower respiratory tract infection and is responsible for 44 per cent of pneumonia deaths in children under 5 years old (World Health Organization, 2025e). Although progress has been made over the last two decades to reduce the number of deaths caused by lower respiratory tract infections related to air pollution in children under 5 (Figure 1), more work to prevent these deaths is needed, especially in LMICs. Children under 5 in sub-Saharan Africa are 100 times more likely to die as a result of air pollution than their counterparts in high-income countries (UNICEF, 2024a). Childhood respiratory diseases linked to

more work to prevent these deaths is needed, especially in LMICs. Children under 5 in sub-Saharan Africa are 100 times more likely to die as a result of air pollution than their counterparts in high-income countries (UNICEF, 2024a). Childhood respiratory diseases linked to the environment Figure 1. Lower respiratory tract infection deaths in children under 5 linked to air pollution exposure, by global region, 2000 and 2021

Note: Mortality among children aged 5–14 years and adolescents aged 15–19 years is much lower in comparison and not shown.

Source: Health Effects Institute (2024, Figure 20).

East, West, Central and Southern Africa South Asia Global Southeast Asia, East Asia and Oceania North Africa and Middle East Central Europe, Eastern Europe and Central Asia Latin America and Caribbean High-income countries 0 50 100 150 200 2000 Lower respiratory tract infection deaths linked to air pollution, rate per 100,000 2021 5Tuberculosis is an infection caused by a specific mycobacterium that often affects the lungs; however , it can spread to various other organs in the body. Tuberculosis is a leading cause of respiratoryrelated morbidity and deaths worldwide. In 2023, approximately 10 million cases of tuberculosis were recorded, with children and young adolescents representing 1.3 million of these cases (World Health Organization, 2024a). As is the case with other lower respiratory tract infections, exposure to tobacco smoke and various household and ambient air pollutants has been linked to an increased risk of tuberculosis (Patra et al., 2015; Xiang et al., 2021). Asthma Asthma is the most common chronic lung disease in children. Childhood asthma has been extensively studied in high-income countries, but less is known about asthma in children living in LMICs. It has been estimated that 10 per cent of children and adolescents around the world have symptoms consistent with asthma. Furthermore, between one third and half of

in children. Childhood asthma has been extensively studied in high-income countries, but less is known about asthma in children living in LMICs. It has been estimated that 10 per cent of children and adolescents around the world have symptoms consistent with asthma. Furthermore, between one third and half of young people with asthma have severe symptoms that regularly interfere with their daily activities (Global Asthma Network, 2022). When a child has asthma, the airways in their lungs can exhibit inflammation, increased mucus production and episodes of reversible airway constriction. Acute asthmatic episodes or ‘asthma attacks’ can be severe and even deadly. Children with asthma can exhibit symptoms like coughing, wheezing (‘whistling’ noise in lungs), chest tightness and trouble breathing. As well as access to life-saving medications that reverse airway inflammation and constriction, a mainstay of asthma management is reducing known environmental asthma triggers. Children with asthma are sensitive to air pollution, as inhalation of various pollutants can lead to asthma symptoms and asthma attacks. Furthermore, evidence suggests that exposure to air pollution in early life puts children at risk of eventually developing asthma (Global Asthma Network, 2022; Health Effects Institute, 2024). Air pollutants, especially those from traffic (see Box 2), as well as ozone, can cause oxidative stress in and injury to the airways, making them more sensitive to asthma triggers, and increase the risk of asthmarelated hospitalization (Aithal et al., 2023). Impaired lung growth and function Measures of a child’s lung function include lung volume (vital capacity) and mechanical function of the airways (such as the forced expiratory volume in 1 second). Research has shown that exposure to air pollution can impact lung function, as assessed by these measures, in children (Garcia et al., 2021). Even prenatal exposure to air pollution is linked to reduced lung function in childhood (Usemann et al., 2024). Decrements in

Research has shown that exposure to air pollution can impact lung function, as assessed by these measures, in children (Garcia et al., 2021). Even prenatal exposure to air pollution is linked to reduced lung function in childhood (Usemann et al., 2024). Decrements in lung function earlier in life can increase the risk of respiratory disease later in life (Aithal et al., 2023; Bush et al., 2024). Upper respiratory tract infections and ear infections Upper respiratory tract infections are very common in children around the world. Symptoms include cough, nasal congestion, sore throat and headache. While most upper respiratory tract infections are selflimited and not fatal, they can decrease quality of life. Sometimes, serious complications can occur , such as pneumonia. Exposure to air pollution and secondhand tobacco smoke can increase the risk of upper respiratory infections by causing oxidative stress and inflammation in the lining of the respiratory tract (Liu et al., 2024). Globally, children under 5 years of age have the highest disability-adjusted life year (DALY) rate for upper respiratory tract infections, especially in countries with a low sociodemographic index score (Jin et al., 2021; Monoson et al., 2023). Upper respiratory tract infections increase the risk of infections of the middle ear (otitis media), which are responsible for significant rates of morbidity in children around the world. Ear infections can lead to issues with hearing and speech and language development, and reduce quality of life. More severe complications can occur , including hearing loss and spread of infection into the cranium. Exposure to tobacco smoke and particulate matter increases the risk of ear infections (Bowatte et al., 2018). Children in LMICs have the highest DALY rate for ear infections (Huang et al., 2024). 6Air pollution is a leading environmental risk factor for respiratory diseases in children. Air pollution is a mixture

particulate matter increases the risk of ear infections (Bowatte et al., 2018). Children in LMICs have the highest DALY rate for ear infections (Huang et al., 2024). 6Air pollution is a leading environmental risk factor for respiratory diseases in children. Air pollution is a mixture of both particles and gases that can impact health when breathed into the respiratory tract. Both anthropogenic and natural sources of air pollution contribute to the burden of respiratory disease (Table 2). Indoor sources of air pollution include fuel burning (cookstoves, heating appliances) and second-hand tobacco smoke. Outdoor sources of air pollution include traffic, waste burning, industrial facilities, wildfires and dust storms. The composition and levels of air pollution vary greatly at the global, regional and local levels owing to the variety of pollution sources and atmospheric conditions. Environmental risk factors for respiratory diseases Air pollutants that can harm the respiratory tract Major sources of air pollution Indoors Outdoors • Particulate matter (PM): • Coarse PM (PM10) • Fine PM (PM2.5) • Ultrafine PM (PM0.1) • Ozone (O3) • Nitrogen oxides (NOx) • Sulfur oxides (SOx) • Volatile organic compounds (VOCs) • Fuel burning for cooking: • Biomass (e.g., wood, dung, charcoal)

• Coal • Kerosene • Liquefied petroleum gas • Tobacco smoke (second-hand smoke)
• Transport • Industrial processes: • Energy generation • Metal smelting • Oil refining • Chemical manufacturing
• Waste burning:
• Household
• Agricultural • Industrial • Wildfires, landscape fires • Sandstorms and dust storms Table 2. Common air pollutants and sources of air pollution that contribute to respiratory disease among children around the world

7Specific air pollutants that impact children’s respiratory health Combustion (burning of fuels such as gasoline, coal or wood) is a significant source of air pollutants, including particulate matter , ozone (O3), nitrogen

disease among children around the world 7Specific air pollutants that impact children’s respiratory health Combustion (burning of fuels such as gasoline, coal or wood) is a significant source of air pollutants, including particulate matter , ozone (O3), nitrogen oxides (NOx) and sulfur oxides (SOx), that have effects on respiratory health. Given the ubiquity and health effects of these pollutants, WHO has released AQGs, which are evidence-based recommendations on limits to the levels of these pollutants that are necessary to protect public health. The guidelines also provide interim targets aimed at enabling countries to take incremental steps towards reducing air pollution levels as they move towards the long-term goal of setting enforceable standards consistent with guideline levels (Table 3). Currently, 128 countries have adopted enforceable air quality standards; however , regulations vary, and few are in line with the WHO AQGs (World Health Organization, 2025c). In recognition of the transboundary nature of air pollution, diverse sources of pollution and various sectors involved, WHO and the United Nations Environment Programme provide support for countries to set air quality standards. A subset of particulate matter called fine particulate matter (PM2.5) is the air pollutant that is the “most consistent and accurate predictor of poor health outcomes” (Health Effects Institute, 2024). It is emitted directly into the air from a source or formed by a chemical reaction in the atmosphere. PM 2.5 consists of microscopic particles less than 2.5 microns in aerodynamic diameter; about 30 of these particles can fit across the width of the average human hair . These microscopic particles are capable of penetrating deep into the lungs and can even be absorbed into the bloodstream and transported around the body. While outdoor PM2.5 levels are decreasing or stabilizing in many regions of the world, 99 per cent of the world’s population live in areas with PM 2.5 levels that are considered ‘unhealthy’ by WHO. Only Finland and

bloodstream and transported around the body. While outdoor PM2.5 levels are decreasing or stabilizing in many regions of the world, 99 per cent of the world’s population live in areas with PM 2.5 levels that are considered ‘unhealthy’ by WHO. Only Finland and Iceland have annual averages that meet the AQG value of no more than 5 µg/m3. Furthermore, 36 per cent of the global population (2.8 billion people) live in areas where PM2.5 levels exceed the least protective interim target (35 µg/m3). Levels of PM2.5 tend to be much higher in LMICs than high-income countries (Health Effects Institute, 2025). As a result, billions of people in LMICs are exposed to PM2.5 at home and outdoors at levels multiple times higher than those recommended by the AQGs (Awe et al., 2022). Air pollutant Averaging time Interim target Air quality guidelineIT-1 IT-2 IT-3 IT-4 Fine particulate matter (PM2.5) (µg/m3) Annual 35 25 15 10 5 24-houra 75 50 37.5 25 15 Coarse particulate matter (PM10) (µg/m3) Annual 70 50 30 20 15 24-houra 150 100 75 50 45 Ozone (O3) (µg/m3) Peak seasonb 100 70 – – 60 8-hour 160 120 – – 100 Nitrogen dioxide (NO2) (µg/m3) Annual 40 30 20 – 10 24-houra 120 50 – – 25 Sulfur dioxide (SO2) (µg/m3) 24-houra 125 50 – – 40 Table 3. Summary of World Health Organization air quality guidelines and interim targets for key air pollutants a 99th percentile (e.g., three to four exceedance days per year).

Sulfur dioxide (SO2) (µg/m3) 24-houra 125 50 – – 40 Table 3. Summary of World Health Organization air quality guidelines and interim targets for key air pollutants a 99th percentile (e.g., three to four exceedance days per year). b Average of daily maximum eight hour mean ozone concentration in the six consecutive months with the highest six-month running average ozone concentration.

Source: World Health Organization (2021).

8Ella Kissi-Debrah was only nine years old when she died of a severe asthma attack in London in 2013. She was the first person to have air pollution listed as contributing to the cause of death, as she lived in a neighbourhood with high levels of traffic-related air pollution. During her 30 visits to health-care providers over the course of two years, no health professional discussed air pollution with the family to highlight the need for any health interventions. According to the coroner’s report, “Air pollution was a significant contributory factor to both the induction and exacerbations of her asthma. During the course of her illness between 2010 and 2013 she was exposed to levels of NO2 and PM in excess of WHO Guidelines. The principal source of her exposure was traffic emissions.” Box 2. Fatal childhood asthma: The landmark case of nine-year-old Ella Common sources of air pollution Household air pollution More than 2 billion people around the world burn solid fuels (e.g., charcoal, wood, crop waste, dung and coal) in open fire pits or inefficient cookstoves. This is common in rural areas of LMICs, especially in sub-Saharan Africa and South Asia, where access to affordable clean cookstoves is limited (International Energy Agency et al., 2025). Indoor fuel burning can release levels of PM2.5 that are 100–1,000 times higher than targets set by the WHO AQGs. As well as releasing PM2.5, fuel burning releases other dangerous pollutants including NOx, SOx, black carbon and volatile organic compounds (VOCs), all

that are 100–1,000 times higher than targets set by the WHO AQGs. As well as releasing PM2.5, fuel burning releases other dangerous pollutants including NOx, SOx, black carbon and volatile organic compounds (VOCs), all of which can affect respiratory health. PM2.5 and nearly 7,000 different compounds (including many cancer-causing agents). Children exposed to second-hand smoke are at risk of lower and upper respiratory tract infections, ear infections and asthma attacks. Second-hand smoke was the eighth largest risk factor for death in children under 5 years in 2021 (meaning 39,000 child deaths could have been prevented if second-hand smoke exposure had been eliminated) (Health Effects Institute, 2024). The burden of disease related to exposure to second-hand smoke is greater in LMICs. No level of exposure to tobacco smoke is safe, and ensuring completely smoke-free indoor spaces is the best way to protect the health of their occupants. While progress has been made with the proliferation of ‘smoke-free’ laws in public indoor spaces, 71 countries continue to allow indoor smoking (World Health Organization, 2023). Smoke-free laws have strong public support, do not harm businesses and improve the health of communities (World Health Organization, 2025a). Traffic-related air pollution Traffic-related air pollution refers to the mixture of air pollutants generated by the exhaust of cars, trucks, buses and other types of vehicles. Diesel engine exhaust is particularly toxic and contains a large amount of ultrafine particulate matter (PM0.1) with metals and organic compounds (Khreis et al., 2020). Although levels of traffic-related air pollution have declined over the past few decades in high-income countries, many low-income areas across the globe continue to face unhealthy levels. Furthermore, air quality improvements from better fuel efficiency and cleaner vehicles have been offset by an increase in the numbers of vehicles on the road (Health Effects Institute, 2024). In 2023, household air pollution was

low-income areas across the globe continue to face unhealthy levels. Furthermore, air quality improvements from better fuel efficiency and cleaner vehicles have been offset by an increase in the numbers of vehicles on the road (Health Effects Institute, 2024). In 2023, household air pollution was responsible for 75 per cent of the 676,000 air pollution-relat