Actually - this is a good example of how our perception is often worse than reality.
I look at it and I can see the scales forming on my top lip (right side as you look at it). The darker pink color isn't normal. Basically the skin was shedding so often in those areas that the underlying skin was pinker and smoother than the rest of my lip. For a while it crossed the vermillion border a little, such that people would tell me my lipstick was smudged.
I wasn't a lip biter. I developed it while trying to heal a crazy hand infection - between the 4th round of Antibiotics and the first antifungal. Thing is, it continued long after my hand healed.