New research from New York Presbyterian Hospital shows that even low exposure to tobacco smoke causes permanent damage to lung tissue, Healthday reported Aug. 20.

Researchers classified 121 people as nonsmokers, active smokers, or low-exposure smokers based on urine-test results. After genetic testing, researchers found that even participants who were very light smokers or exposed only to secondhand smoke exhibited cell damage to the small airway.

“We found that if we could detect nicotine in the urine we could also detect changes in the genes in the cells lining the airways,” said Ronald Crystal, M.D., chief of the division of pulmonary and critical care medicine at New York-Presbyterian and co-author of the study.

“There is no level of cigarette smoking or exposure to cigarette smoke that does not make the cells in your lungs sick,” said Crystal. “Don't think that smoking one or two cigarettes a week means you are home free.”

The study was published online on Aug. 6 in the American Journal of Respiratory and Critical Care Medicine.