Nicotine is the addictive substance found in tobacco plants. Benzoic acid can also be naturally present in crops, 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 lining of the lungs. One small clinical examine from 2018 that found 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 modifications have been linked to bronchial asthma. Sign up for our Health Tip of the Day e-newsletter, and receive day by day suggestions that will help you reside your healthiest life.