Breastfeeding Duration and Airway Inflammation in Children With Asthma Living in a Polluted Megacity

Background Children with asthma living in highly polluted megacities are at increased risk of poor asthma control and airway inflammation. Breastfeeding has immunomodulatory effects, but its potential to buffer pollution‐related inflammation remains understudied. Objective To evaluate whether breastfeeding duration is associated with asthma control and airway eosinophilic inflammation (FeNO), and whether it modifies the impact of urban air pollution in children with asthma living in Mexico City. Methods We conducted a multicenter retrospective study (2022–2025) including children aged 6–17 years with physician‐diagnosed asthma. Asthma control (ACT), airway inflammation (FeNO, NIOX VERO), breastfeeding duration (0–12 months), and borough‐level pollution categories (high/medium/low) were evaluated. Multivariable logistic and linear regression models assessed associations and breastfeeding × pollution interactions. Results A total of 162 children were included (mean age 10.8 years; 51.2% female). Breastfeeding ≥ 6 months was associated with better asthma control (ACT ≥ 20: OR 2.1; 95% CI 1.3–3.5) and significantly lower FeNO (β −0.24; p < 0.01). High‐pollution residence was linked to lower ACT scores and higher FeNO (both p < 0.01). A significant interaction indicated that breastfeeding ≥ 6 months attenuated the detrimental effect of pollution on airway inflammation and asthma control ( p for interaction < 0.05). Conclusions Prolonged breastfeeding was independently associated with improved asthma control and reduced airway eosinophilic inflammation, partially mitigating the respiratory burden of chronic pollution exposure. Clinical Implications Breastfeeding may serve as an accessible, low‐cost protective strategy for children with asthma living in polluted urban environments, supporting its integration into respiratory health policies and early‐life preventive care.