It goes without saying that smoking is just about the worst thing you can do to your lungs. Recent research confirms that quitting is what matters—not just cutting back. (Long-term light smoking still carries a high risk for lung disease.) The good news is, if you quit before 35, your lungs can typically recover by age 50.
And it's not only cigarettes. Vaping, while touted as a "safer" alternative to cigarettes, has been associated with a disease called "wet lung" even in teens. Studies that look at the link between smoking marijuana and lung disease have been less definitive.