I have a relative who doesn’t smoke but developed COPD nevertheless. I thought this disease was caused by smoking, so how did she get it?

Nonsmokers can develop chronic obstructive pulmonary disease (COPD), which includes several diseases—emphysema, chronic bronchitis, and some types of asthma—that can obstruct airflow from the lungs and make breathing harder. Although being a smoker is the biggest risk factor for COPD, it’s estimated that people who have never smoked represent about 25 percent of those who have the disease. (The percentage runs higher in developing countries where respiratory exposure to toxins is more common.)

Secondhand cigarette smoke is a common culprit in the development of COPD in never-smokers, but researchers also point to occupational and environmental toxins. Jobs involving exposure to various kinds of dust and gases, such as farming, milling, mining, steelwork, welding, firefighting, and dry cleaning, appear to contribute to the problem. In developing countries, cooking with solid fuels such as wood, charcoal, and peat is a major contributor for women.

Most people who have COPD are older, with incidence rising with age. Among all age groups, however, women are disproportionately affected by COPD; this is true of never-smokers as well as smokers. Some research suggests that women’s smaller average lung size may put them at greater risk for damage from exposure to any smoke or other toxin. And differences in the way women and men process cigarette smoke may make it more toxic to women. Hormonal factors could play a role as well.

Other never-smokers more likely to be afflicted with COPD are people with frequent respiratory symptoms and childhood breathing problems. About 1 percent of people with COPD have a genetic mutation called alpha-1-antitrypsin deficiency that can result in emphysema.

If you’re experiencing wheezing, frequent shortness of breath, or a cough that won’t quit, see your doctor. While medications can reduce symptoms, the most important intervention is to eliminate exposure to the tobacco smoke or other toxins that are causing COPD. For people with more severe COPD, participating in a pulmonary rehabilitation program can improve exercise tolerance and quality of life.