Nicotine is the addictive substance present in tobacco crops. Benzoic acid can also be naturally found in plants, and is used commercially in dyes, perfumes, insect repellants, and meals preservatives. Existing cell, animal, and medical research recommend that glycerin and propylene glycol irritate the liner of the lungs. One small scientific study 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 changes have been linked to asthma. Sign up for our Health Tip of the Day newsletter, and obtain day by day suggestions that will assist you to live your healthiest life.