Nicotine is the addictive substance present in tobacco plants. Benzoic acid can also be naturally present in plants, and is used commercially in dyes, perfumes, insect repellants, and meals preservatives. Existing cell, animal, and clinical studies counsel that glycerin and propylene glycol irritate the lining of the lungs. One small medical study from 2018 that discovered that the compounds changed vapers’ sputum—the mucosal lining that covers the interior respiratory tract—to specific different immune proteins. Some of those protein changes have been linked to bronchial asthma. Sign up for our Health Tip of the Day publication, and obtain daily ideas that can help you reside your healthiest life.