Nicotine is the addictive substance present in tobacco plants. Benzoic acid is also naturally found in crops, and is used commercially in dyes, perfumes, insect repellants, and meals preservatives. Existing cell, animal, and medical research recommend that glycerin and propylene glycol irritate the liner of the lungs. One small scientific examine from 2018 that found that the compounds changed vapers’ sputum—the mucosal lining that covers the interior respiratory tract—to express completely different immune proteins. Some of those protein modifications have been linked to asthma. Sign up for our Health Tip of the Day e-newsletter, and receive day by day ideas that will help you stay your healthiest life.