In contrast to combustion smoke, the aerosol (mist) formed by e-cigarettes does not contain solid particles (tar), but rather liquid droplets that cannot settle in the lungs. The substances dissolved in the droplets are exhaled or absorbed by the epithelial cells (oral mucosa, respiratory tract). Clinical studies show that switching from smoking to vaping improves lung function in people with bronchial asthma or COPD and that years of vaping have no effect on lung function in non-smokers. The nature of the aerosol from e-cigarettes is physically identical to aerosols that are used for inhalation therapy of lung diseases. The smaller the liquid droplets in the aerosol, the deeper they penetrate into the lungs. Deep penetration into the lungs promotes the absorption of dissolved substances, but does not result in the droplets having any harmful effect on health. It is clinically irrelevant whether the droplets dissolve in the upper respiratory tract or in the bronchioles.
Quoted from: KARL FRANZENS UNIVERSITY GRAZ INSTITUTE OF PHARMACEUTICAL SCIENCES - Pharmacology and Toxicology - Head: 0. Univ.-Prof. Dr. Bernhard Michael Mayer