Thrush could very well be a culprit an infection, of some sort - or a mechanical injury when we skin our knee we scab, on an injured tongue its a milky white patch that eventually goes away when the area is healed. Also lichen planus.

Speaking of which someone mentioned leaving lichen planus too long to be treated and this leading to cancer. I have to say don't beat yourself up. Seriously. As far as I know they do not know what causes lichen planus, therefore treatment is not really a happening thing. I mean unless there have been recent discoveries since I was diagnosed - I was originally told lichen planus, then the biopsy confirmed cancer, but I did a bit of research into lichen planus, and from what I read treating it is a crap shoot. And not all lichen planus turns into cancer.

Hugs.