Smoking is the culprit of chronic obstructive lung disease – everybody knows that. Except when it isn’t. While smoking remains the major cause of COPD – the combined term for emphysema, bronchitis and some forms of asthma – about one-quarter of people affected are nonsmokers. Some have a genetic form of COPD. And for others, environmental factors play a role.

“There’s very strong evidence that if you’re exposed to vapors, dust, gas and fumes at the workplace, then you have increased risk of COPD – independent of smoking,” says Dr. John Balmes, a professor with the University of California–San Francisco medical school and at the UC–Berkeley School of Public Health.