Original Research
Environmental Health

Indoor Air Quality and Its Association With Respiratory Health Among Preschool Children in Urban and Suburban Areas

Background and Context

Children spend a substantial proportion of their waking hours indoors — in homes, childcare centres, and preschools — making indoor air quality (IAQ) a critical determinant of paediatric respiratory health. Young children are particularly vulnerable to air pollutants due to their higher respiration rates relative to body weight, still-developing lungs, and tendency to breathe through their mouths, which bypasses the nasal filtration that provides partial protection in adults. The World Health Organization has estimated that 3.2 million deaths globally are attributable to household air pollution, including over 237,000 deaths among children under five years of age.

In Malaysia, preschool attendance has expanded significantly over recent decades, with millions of children spending six or more hours daily in these environments. The quality of indoor air in Malaysian preschools is influenced by building design, ventilation systems, proximity to traffic, cooking activities, cleaning products, and the tropical climate’s interaction with humidity and temperature. Despite these concerns, systematic research on IAQ in Malaysian preschools — and its direct association with children’s respiratory health — remained limited when this study was conducted.

The urban–suburban divide in air quality is well-documented globally. Urban environments typically experience higher concentrations of traffic-related pollutants, including particulate matter, nitrogen dioxide, carbon monoxide, and volatile organic compounds. When these outdoor pollutants infiltrate indoor spaces with inadequate ventilation, the resulting indoor concentrations can exceed outdoor levels. This study specifically examined whether the urban–suburban gradient in outdoor air quality was reflected inside preschool classrooms and whether it was associated with differential respiratory outcomes among the attending children.

Study Design and Methods

This cross-sectional study was conducted in preschools located across Shah Alam and Hulu Langat in Selangor, Malaysia, representing urban, suburban, and rural settings. The study employed a two-pronged approach: direct measurement of indoor air pollutants in preschool classrooms and assessment of respiratory health symptoms among the attending children.

Indoor air quality parameters were measured using calibrated direct-reading instrumentation placed at the centre of classrooms during operational hours. The parameters assessed included carbon monoxide (CO), particulate matter of two size fractions (PM₁₀ and PM_2.5), volatile organic compounds (VOCs), carbon dioxide (CO₂), temperature, and relative humidity. Measurements were compared against established IAQ standards, including those set by the Malaysian Department of Occupational Safety and Health (DOSH) Industry Code of Practice on Indoor Air Quality (2010) and international guidelines from ASHRAE.

Respiratory health data were collected through validated questionnaires completed by parents or guardians, assessing the prevalence and frequency of symptoms including cough, wheezing, breathlessness, nasal congestion, and chest tightness. Sociodemographic and environmental exposure data — including household smoking status, presence of pets, type of cooking fuel, and history of respiratory illness — were also collected to enable adjustment for potential confounders.

Principal Results

The IAQ measurements revealed statistically significant differences between preschool locations for multiple pollutant parameters. Urban area preschools consistently recorded the highest concentrations of CO, PM₁₀, and PM_2.5. The differences in particulate matter concentrations are particularly concerning given the well-established association between fine particulate exposure and adverse respiratory outcomes in children, including exacerbation of asthma and increased susceptibility to respiratory infections.

Respiratory symptom analysis demonstrated that children attending urban preschools had significantly higher prevalence of cough and wheezing compared with their counterparts in suburban and rural settings. The chi-square test results for cough (χ² = 25.462, p = 0.001) and wheezing (χ² = 27.299, p = 0.001) indicated robust statistical associations that were unlikely to be attributable to chance.

Further statistical analysis revealed significant associations between specific indoor pollutants and respiratory symptoms. Cough was associated with indoor concentrations of CO, PM₁₀, and PM_2.5, suggesting that the elevated pollutant levels in urban preschools were contributing to the increased respiratory morbidity observed among their students. These findings are consistent with the broader literature on indoor air pollution and children’s respiratory health, which has identified particulate matter and combustion by-products as key risk factors for respiratory symptoms in young children.

The Malaysian Indoor Air Quality Landscape

Malaysia’s tropical climate creates unique challenges for indoor air quality management. High ambient temperatures and humidity levels — often exceeding 80% relative humidity — promote the growth of biological contaminants including mould and dust mites, both known triggers for respiratory symptoms and asthma exacerbation. Many preschools in Malaysia rely on natural ventilation through open windows, which can introduce outdoor pollutants while also depending on adequate air circulation to dilute indoor-generated contaminants.

In urban areas such as Shah Alam, proximity to major roadways and industrial zones means that outdoor air quality is frequently compromised. When preschools are located near busy roads, the infiltration of traffic-related pollutants into indoor spaces can be substantial. Additionally, many preschools in Malaysia include on-site cooking facilities that can generate significant levels of particulate matter and combustion gases, further degrading indoor air quality.

The Malaysian DOSH Industry Code of Practice on Indoor Air Quality (2010) provides guidelines for acceptable levels of various indoor pollutants in buildings, including limits for CO₂ (1,000 ppm ceiling concentration), CO, and particulate matter. However, enforcement and compliance in childcare settings has been variable, and many preschool operators may lack awareness of IAQ standards or the resources to implement appropriate ventilation improvements.

Implications for Child Health Policy

These findings carry significant implications for Malaysian child health and environmental policy. The demonstrated association between indoor air pollutant levels and respiratory symptoms in preschoolers provides evidence to support stronger IAQ regulation in early childhood education settings. Specific policy recommendations emerging from this research include mandatory IAQ monitoring in licensed preschools, minimum ventilation standards tailored to the Malaysian climate, guidelines on preschool siting to minimise proximity to major pollution sources, and training for preschool operators on IAQ management practices.

From a clinical perspective, the findings reinforce the importance of considering environmental exposures when evaluating respiratory symptoms in young children. Paediatricians and family physicians should enquire about the preschool environment when assessing children with recurrent cough, wheezing, or respiratory infections, and consider recommending IAQ assessment where concerns are identified.

Limitations

The cross-sectional design limits causal inference — while associations between IAQ parameters and respiratory symptoms were identified, it is not possible to definitively establish that the observed pollutant levels caused the respiratory symptoms. Respiratory health data were based on parental report rather than clinical examination or lung function testing, introducing potential recall and reporting bias. The study did not measure all relevant indoor pollutants (such as formaldehyde and nitrogen dioxide), and measurements were taken during operational hours, which may not capture the full range of IAQ conditions experienced by children. Additionally, individual-level exposure assessment was not performed — classroom-level measurements serve as proxies for personal exposure but do not account for the time children spend in other indoor environments including their homes.

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