Nicotine is the addictive substance found in tobacco vegetation. Benzoic acid can also be naturally found in crops, 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 clinical research from 2018 that discovered that the compounds changed vapers’ sputum—the mucosal lining that covers the inner respiratory tract—to express 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 daily tips that will allow you to stay your healthiest life.