Glycerin is harmless. Registered as a food additive E422 as an emulsifier and viscosity stabilizer. It also participates in many metabolic processes in the body.
With rare use as inhalations by allergy sufferers, none have been recorded. With constant use by "vapors" - also none.
True, the second, the result of not very large local studies in Kazakhstan and slightly larger ones in the states. I think after a while we will wait for more accurate and real data. Until then.