Nicotine is the addictive substance present in tobacco crops. Benzoic acid can also be naturally found in crops, and is used commercially in dyes, perfumes, insect repellants, and food preservatives. Existing cell, animal, and scientific studies suggest that glycerin and propylene glycol irritate the liner of the lungs. One small scientific research from 2018 that found that the compounds changed vapers’ sputum—the mucosal lining that covers the interior respiratory tract—to specific totally different immune proteins. Some of those protein modifications have been linked to asthma. Sign up for our Health Tip of the Day publication, and obtain daily suggestions that will help you reside your healthiest life.