Nicotine is the addictive substance present in tobacco plants. Benzoic acid can be naturally found in plants, and is used commercially in dyes, perfumes, insect repellants, and meals preservatives. Existing cell, animal, and scientific research suggest that glycerin and propylene glycol irritate the liner of the lungs. One small scientific research from 2018 that found that the compounds changed vapers’ sputum—the mucosal lining that covers the internal respiratory tract—to specific different immune proteins. Some of these protein modifications have been linked to bronchial asthma. Sign up for our Health Tip of the Day publication, and obtain daily ideas that can help you reside your healthiest life.