Nicotine is the addictive substance present in tobacco vegetation. 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 clinical studies recommend that glycerin and propylene glycol irritate the lining of the lungs. One small medical examine 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 modifications have been linked to bronchial asthma. Sign up for our Health Tip of the Day newsletter, and obtain daily suggestions that will help you stay your healthiest life.