Why does the Vermillion Border fade? Can it be regrown/repaired?

Why does the Vermillion border fade (scientifically) and can it ever actually be regrown/repaired or are there just illusion procedures to make it appear defined? Is there a reason one portion might fade faster/more than another? (ex: one side the Cupid's Bow). Is it possible to have definition go away but not have much thinning or wrinkle issues? If so, what might be the best mitigation?