Nicotine is the addictive substance present in tobacco plants. Benzoic acid can also be naturally found in vegetation, and is used commercially in dyes, perfumes, insect repellants, and food preservatives. Existing cell, animal, and clinical studies recommend that glycerin and propylene glycol irritate the lining 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 express totally different immune proteins. Some of those protein modifications have been linked to asthma. Sign up for our Health Tip of the Day newsletter, and receive every day suggestions that can assist you to live your healthiest life.