Nicotine is the addictive substance found in tobacco crops. Benzoic acid can also be naturally present in vegetation, and is used commercially in dyes, perfumes, insect repellants, and meals preservatives. Existing cell, animal, and clinical research counsel that glycerin and propylene glycol irritate the lining of the lungs. One small clinical study from 2018 that discovered 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 modifications have been linked to asthma. Sign up for our Health Tip of the Day newsletter, and receive every day ideas that can assist you to live your healthiest life.