What Causes White Blister In Middle Of Lip?

Hi, I woke up with a white blister in the middle of my upper lip this morning. It has never happened before and I just got a bunch of tests done about a month ago including the herpes test. All came out negative. I have been going to a tanning bed for a while now and was wondering if it could be A burn because I use chap stick all the time. Please help. And what will get rid of it? I am 5.8" 163 lbs. No med history of anything like this and do not have a fever or any ilnesses