Here is my theory. I used to have stomach pains and I think this could be Inflammatory bowel syndrome. There is a new hypothesis that I found on wikipedia that says IBD could be caused by overactive immune system attacking various tissues of the digestive tract because of the lack of traditional targets such as parasites and worms. Prebiotics and probiotics are showing increasing promise as treatments for IBD. So you are feeding your body organisms so your immune system attacks them rather than your lips? I think there is an inner reason why our lips are like this and I think it has something to do with IBD.