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Asthma and chronic obstructive pulmonary disease (COPD) are among the most common chronic respiratory illnesses, with considerable overlap in older adults.1 Patients with features of both often face accelerated lung function decline, frequent exacerbations and poorer survival.2 Understanding why some patients with asthma progress to COPD has long been a challenge. In this issue of Thorax, Li and colleagues provide timely evidence implicating long-term air pollution exposure and genetic susceptibility in shaping this trajectory.3