Nicotine is the addictive substance present in tobacco vegetation. Benzoic acid can be naturally present in vegetation, and is used commercially in dyes, perfumes, insect repellants, and food preservatives. Existing cell, animal, and medical studies counsel 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 specific different immune proteins. Some of these protein adjustments have been linked to bronchial asthma. Sign up for our Health Tip of the Day publication, and receive day by day tips that can allow you to live your healthiest life.