Mouth to Lung (MTL) Vs Direct Lung (DL) Inhale Explained E Cigarette Direct Vaping, Even Without Nicotine, Has Negative Effect on Lungs What is MTL & DTL Vaping? Key Differences for Beginners! New lung scans prove vaping is toxic. The science is officially in. Scans show that teens have developed "popcorn lung" as a result of vaping. It's a permanent, chronic disease that shortens