When you bite ur lip y does it turn white and how do u get rid of it ?

It hurts bad too?: We don't really know what causes aphthous ulcers, but they tend to be hereditary--likely some autoimmune process. They often occur at the site of trauma, in your case is lip-biting, and after a couple of days they turn into shallow-white-based ulcers which can hurt quite a bit. Topical steroid paste or rinse may help, but they will go away with or without treatment. Consult doc. Good luck.