Nicotine is the addictive substance found in tobacco vegetation. Benzoic acid can also be naturally found in crops, and is used commercially in dyes, perfumes, insect repellants, and meals preservatives. Existing cell, animal, and clinical studies suggest that glycerin and propylene glycol irritate the liner of the lungs. One small scientific examine from 2018 that discovered that the compounds modified vapers’ sputum—the mucosal lining that covers the interior respiratory tract—to express different immune proteins. Some of these protein modifications have been linked to bronchial asthma. Sign up for our Health Tip of the Day publication, and obtain day by day tips that will help you stay your healthiest life.