Is the Propylene Glycol in e-cigarettes bad for you?

I know that the two main ingredients in the cartridges in Electronic cigarettes is Nicotine, and propylene glycol. My uncle is a dentist so he knows a fair amount about a lot of medical stuff, but mostly oral stuff. He says that he thinks that the propylene glycol may be hazardous. Is that true? Or did he misunderstand something. I’m 19 and have been thinking about switching to blu-cigs, so any information would be helpful. Thanks!

Causes mild eye irritation. Contact may cause irritation, tearing, and burning pain.
Causes moderate skin irritation. Contact with the skin may cause erythema, dryness, and defatting.
May cause gastrointestinal irritation with nausea, vomiting and diarrhea. Low hazard for usual industrial handling. May cause hemoglobinuric nephrosis. May cause changes in surface EEG.
Low hazard for usual industrial handling. May cause respiratory tract irritation.