Most of it or all of it is water based, i'd say all of it. It is probably labeled "GRAS" - Generally regarded as safe... This translates to don't drink it or inject it and you probably won't die.
found this from one manufacturer:
"Our fluid is a mixture of USFDA food grade glycols found in make-up, cough syrup, etc… This juice is a heavy unscented mixture that has an extremely long hang time. It also provides a self cleaning action in fog machines.
The fog juice is a proprietary mixture of very low toxicity ingredients. All major components are essentially non-toxic if ingested. They are generally regarded as SAFE by the U.S. Food and Drug Administration (FDA), and have been individually approved for use in foods, food additives or pharmaceutical preparations.
SAFE TO USE... At the arenas where we have talked to the center owners they tell us that they have had virtually no complaints from their kids who have asthma or other breathing disorders.
As long as they don’t let the kids run, which causes problems with asthma...there doesn’t seem to be any problems, is the consensus."
