I'm not sure how I got it. But after reading other people's experiences, I think it was probably from picking at my dry lips. I remember that a couple of times I pulled a fairly big chunk and I drew blood. The dryness got much worse after that, and then the crusting, curling up and peeling cycle began. I wish I had known what I know now. :(
But then again, the cause could've been a dozen of other things: mint/menthol, some new supplements I started, a couple of new foods. Who knows.
I spent a lot of time trying to figure out the cause, but then I just decided that it didn't matter so much to me, and that it was more important to find a solution. I tried a couple of other things (without success) before this borax/hp/lanolin protocol. Doing great so far, so I think this will be successful for the long term.