What Causes Tree Bark Skin On Butt Crack?

I ve had this (tree) bark looking growth above the butt crack, like at the end of the tail bone. It is now about 2 up the crack. At first, I thought it looked like a type of moss (I know that sounds weird), but the more it grew, it has started to look like soft tree bark. After showering, that growth becomes soft but does not come off (I ve tried scraping to see if that would work. Nope.) I have to watch how I sit or how I lie in bed so I don t irritate it because it s uncomfortable. Not hurting, just very uncomfortable. This has been accompanied by (a few times) a discoloration on the butt cheeks itself that looks like bruising that would scale over and fall off and eventually go away. This is so embarrassing.