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