I was wondering what the cause of this usually is, and how to fix it
All people have facial asymmetry, and this will often present in mild lip, a symmetry as well.During embryological development, the upper lip forms as three separate segments that eventually fuse.Anatomically, we usually view the upper lip as having three segments and the lower lip as having a left and right segment. Failure of complete lip fusion leads to malformations like a cleft lip.Your lip looks pretty normal in the pictures you’ve included.I don’t see any need for intervention.Best,Mats Hagstrom MD