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