I haven't experienced this. Actually, to the contrary I used to get white blisters on my lips when I smoked cigarettes... Always where the cigs touched my lips (usually in the center). A very small percentage of the population experiences a mild allergic reaction to Propylene Glycol. The symptoms of that mild allergic reaction usually includes itching, rash, and irritation. If you are one of those rare people who react to PG then it makes sense that it may cause some mouth sores when you vape:( To test this try using a pure VG Juice just to see... A bit too sweet for my taste but could probably adjust if needed. Good Luck!