I found some information on inhaling vegetable oil although some of it maybe outdated, and just for the record, I'm not trying to cherrypick any sources
From the information I've found, it seems that vegetable oil doesn't actually cause liquid pneumonia, such as suspected in
this post on ECF, but it does seem to induce liquid pneumonia-like symptoms by creating a mucous layer on your lungs that your body doesn't have time to expel if you are vaping only oil-flavored liquids. I came to this conclusion because pneumonia is an infection but oil shouldn't be causing any infections especially since there is VG in the liquid, which is bacteriostatic, and in some liquids PGA, which kills the bacteria outright.
"Oily inhalation (most often of vegetable oil with menthol) is used for therapeutic and prophylactic purposes; a thin, oily film is formed on the mucosa of the upper respiratory tract, which inhibits absorption of various toxic substances and promotes their expectoration." The Great Soviet Encyclopedia, 3rd Edition (1979)
"Most vegetable oil mists are biologically inert and are therefore considered to be nuisance particulates. Vegetable oil mists seem to have little adverse effect on the lungs and do not produce significant organic disease or toxic effects when exposures are kept under reasonable control" OSHA - [ACGIH 1991]
"What are the symptoms?
Symptoms of pneumonia
caused by bacteria usually come on quickly. They may include:
Cough. You will likely cough up mucus (sputum) from your lungs." - WebMD
"What causes pneumonia?
Germs called bacteria or viruses usually cause pneumonia.
Pneumonia usually starts when you breathe the germs into your lungs. You may be more likely to get the disease after having a cold or the flu. These illnesses make it hard for your lungs to fight infection, so it is easier to get pneumonia. Having a long-term, or chronic, disease like asthma, heart disease, cancer, or diabetes also makes you more likely to get pneumonia. " - WebMD
