Nicotine is the addictive substance found in tobacco crops. Benzoic acid can also be naturally found in plants, and is used commercially in dyes, perfumes, insect repellants, and meals preservatives. Existing cell, animal, and clinical studies counsel that glycerin and propylene glycol irritate the liner of the lungs. One small clinical study from 2018 that found that the compounds changed vapers’ sputum—the mucosal lining that covers the interior respiratory tract—to precise different immune proteins. Some of those protein modifications have been linked to bronchial asthma. Sign up for our Health Tip of the Day newsletter, and receive every day tips that may allow you to reside your healthiest life.