Three-quarters of chronic obstructive pulmonary disease (COPD) cases have their origins in poor lung function pathways beginning in childhood. These pathways are associated with exposures in childhood, and amplified by factors in adulthood, according to a cohort study. While smoking remains the biggest risk factor for COPD, the study demonstrates that childhood illnesses (such as asthma, bronchitis, pneumonia, allergic rhinitis, eczema) and exposures to parental smoking are also linked to the disease.