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