Of course, its definitely Sun Damage.
As I have posted before. My condition is like DFX, not huge crusts or anything, just a contunial peeling.
My view it is all caused by a combination of things. Initial wearing down of the skin layers by Kissing hard and then by all the added attention given to the lips once the condition was discovered by me. Then they had very little protective barrier. A couple of memorable sun burn experiences where they blistered up very bad. Then the protection was gone altogether and the lips become effected by all sorts of things.
For me Sun Damage was the real main cause of what I have today. The UV changes the DNA in the skin cells, causing them to never heal in the way nature intended.