Nicotine is the addictive substance present in tobacco vegetation. Benzoic acid can also be naturally found in vegetation, 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 liner of the lungs. One small clinical research from 2018 that found that the compounds modified vapers’ sputum—the mucosal lining that covers the internal respiratory tract—to express completely different immune proteins. Some of those protein adjustments have been linked to asthma. Sign up for our Health Tip of the Day newsletter, and receive daily suggestions that can allow you to live your healthiest life.