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