Secondhand smoke has been classified as a known cause of lung cancer in humans (Group A carcinogen).
Update Date 8/31/2014
Updated by: Yi-Bin Chen, MD. Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.