When compared to actors from the non-"smoke" productions, actors from two or more of the four productions utilizing theatrical "smoke" reported experiencing a significantly greater prevalence of nasal symptoms (sneezing, runny or stuffy nose), respiratory symptoms (cough, wheeze, breathlessness, chest tightness), and mucous membrane symptoms (sore throat, hoarseness, dry throat, itchy/burning eyes, dry eyes) during their performances for the week prior to the survey.
The final line is: The quantity and frequency of use of the various fogs during a performance should be minimized.
PS: A method of action was suggested to be the breakdown of glycol due to high temperature.
Fog machines cause noticeable effects on breathing at significantly lower exposure levels and concentrations than vaping. IOW, it provides a lower bound for the purported safety of vaping.
> Based on the results of this study, there is no evidence that theatrical "smoke," at the levels found in the theaters studied, is a cause of occupational asthma among performers.
That being said, chronic exposure is probably not good for you. From a health perspective, don't inhale anything other than air!