If you are allergic to PG, or it irritates you, this will cause a TH, as will any irritating flavor. TH is from anything vapor that the lungs and throat are having a hard time with. Its a natural defense response of your body asking you "What was THAT??" Things that can cause the TH are: PG, alcohol, nic, a juice-starved atty coil, some flavors. Some people really want a lot of TH, but it is not necessarily something one should try to enhance a lot, IMHO, as it means the throat and lungs don't like it.