Nicotine is the addictive substance present in tobacco crops. Benzoic acid is also naturally found in crops, 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 research from 2018 that discovered that the compounds modified vapers’ sputum—the mucosal lining that covers the inner respiratory tract—to precise different immune proteins. Some of those protein changes have been linked to bronchial asthma. Sign up for our Health Tip of the Day e-newsletter, and receive every day tips that may allow you to reside your healthiest life.