The Multiple Breath Washout (MBW) will be used to determine whether youth who vape nicotine have lung damage compared to the controls who do not vape nicotine and who do not smoke traditional cigarettes. The MBW is an easy-to-perform test that measures how efficiently an individual’s lungs work. The main outcome is the lung clearance index (LCI) which has been shown to identify early signs of lung disease, specifically in the small airways. While not previously used to study e-cigarette use, we hypothesize that the LCI can identify early-stage lung damage and provide urgently needed objective evidence of potentially deleterious effects of e-cigarette use. In the first phase of the study young adults between the ages of 18 and 24 are eligible to participate if they vape, and do not have a history of lung disease. In the second stage we will expand the eligibility criteria to include adolescents between the ages of 16 and 18.