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