Nicotine is the addictive substance present in tobacco vegetation. Benzoic acid is also naturally present in plants, and is used commercially in dyes, perfumes, insect repellants, and meals preservatives. Existing cell, animal, and clinical studies recommend that glycerin and propylene glycol irritate the lining of the lungs. One small medical examine from 2018 that found that the compounds changed vapers’ sputum—the mucosal lining that covers the inner respiratory tract—to express different immune proteins. Some of those protein adjustments have been linked to asthma. Sign up for our Health Tip of the Day publication, and receive every day tips that can help you reside your healthiest life.