not-yet-known not-yet-known not-yet-known unknown Preterm birth Preterm birth is associated with smaller airways, reduced lung function and increased risk of wheezing disorders, particularly very preterm. In the study by Kotecha et al,4 at 8–9 years of age, late preterm (GA 33–34 wk) had FEV1, forced expiratory flow at 25–75% of forced vital capacity (FEF25–75) and FEV1/FVC ratio comparable to that in children born at 25–32 weeks, but significantly lower than in children born at term. The possible mechanisms included the triggers of preterm birth namely maternal smoking, restricted growth, and inflammation. Prematurity thus has direct negative impacts on lung development, airway reactivity, and immune responses. ‘Unclean’ cooking fuel use and air pollution Oguonu et alr5 showed the impact of cooking fuels/biomass exposure on lung function in children in households in South-East Nigeria, and noted poor lung function in the exposed children more in rural dwellings. Cohort studies have also shown environmental air pollution to affect lung growth. Long-term exposure to small particulate matter and nitrogen dioxide significantly lower growth in FVC and FEV1 during school-age.1 Another study showed that high traffic exposure at birth was associated with transient and persistent wheeze but only high average exposure from birth through to age 7 years was associated with school-age asthma, thus suggesting cumulative dose is important.6 In a meta-analyses of traffic-related air pollution, 41 studies found significant associations between asthma beyond 6 years and prior exposure to black carbon, nitrogen dioxide and particulate matter. The Case– control registry study of all Danish children born between 1997 and 2014 showed a significant association with increased 12-month average particulate matter and nitrogen dioxide exposure linked to risk of persistent wheezing in children <6 years.7