Nicotine is the addictive substance found in tobacco plants. Benzoic acid is also naturally present in plants, and is used commercially in dyes, perfumes, insect repellants, and food preservatives. Existing cell, animal, and clinical studies suggest that glycerin and propylene glycol irritate the lining of the lungs. One small medical research from 2018 that found that the compounds modified vapers’ sputum—the mucosal lining that covers the inner respiratory tract—to precise totally different immune proteins. Some of those protein modifications have been linked to asthma. Sign up for our Health Tip of the Day publication, and receive day by day ideas that will allow you to stay your healthiest life.