Electronic cigarette (E-cigarette) is a term that usually refers to a kind of electronic product that imitates traditional cigarettes in terms of their appearance, taste, aroma and other aspects. They are powered by batteries, conveying nicotine to the respiratory system via a heating or atomizing method, which leads to the same physiological and psychological feeling as traditional cigarettes . In 2014, the World Health Organization (WHO) defined devices that could release nicotine (also known as E-cigarettes) as products that suck nicotine aerosol through a cigarette holder or other components .