E cigarettes and the ob gyn: Key safety information for prenatal counseling Contemporary OB GYN Researchers at the University of California, Riverside, found that heating propylene glycol, the main ingredient in most e cigarette liquids, can produce two toxic chemicals, methylglyoxal and acetaldehyde, which damage lung cells. Using Liquid E Cigarettes Liquid nicotine used in e cigarettes still a danger to children despite recent Toxicity and Appeal of Flavoured E Cigarettes and Flavour Ban Outcomes: A Narrative Review