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