> no known negative effects from inhaling glycerin vapours

From https://www.banyantreatmentcenter.com/2022/01/10/vaping-vegetable-glycerin-side-effects/ :

> Researchers have recently found that vegetable glycerin can lead to inflammation of the lungs due to long-term vaping or e-cigarette use. One study on the dangers of vaping glycerin ran for four weeks, during which 34 were randomized to using flavor- and nicotine-free e-cigs or to a control group of no-use. At the end of the study, researchers discovered that the side effects of inhaling vegetable glycerin included inflammation in the lungs. The study also found that those who smoked e-cigarettes twice a day for a month contained higher levels of chemicals like propylene glycol in their blood.1

Also see https://www.news-medical.net/news/20191018/Vaping-propylene-glycol-and-vegetable-glycerine-may-lead-to-lung-inflammation.aspx