Nicotine is the addictive substance present in tobacco crops. Benzoic acid is also naturally present in plants, and is used commercially in dyes, perfumes, insect repellants, and food preservatives. Existing cell, animal, and scientific research suggest that glycerin and propylene glycol irritate the lining of the lungs. One small scientific examine from 2018 that discovered that the compounds modified vapers’ sputum—the mucosal lining that covers the inner respiratory tract—to express totally 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 receive day by day suggestions that may allow you to reside your healthiest life.