Nicotine is the addictive substance present in tobacco crops. Benzoic acid can be naturally found in vegetation, and is used commercially in dyes, perfumes, insect repellants, and food preservatives. Existing cell, animal, and clinical research counsel that glycerin and propylene glycol irritate the lining of the lungs. One small scientific research from 2018 that found that the compounds changed vapers’ sputum—the mucosal lining that covers the interior respiratory tract—to express different immune proteins. Some of those protein changes have been linked to asthma. Sign up for our Health Tip of the Day newsletter, and obtain day by day ideas that will assist you to stay your healthiest life.