Thumbsticks have little bumps all over them?

I've had my Vita since mid-October and I have played it quite a bit since then. I'd say in total around 500 hours of logged, in-game playtime (Not excluding deaths and menu stuff, this is just from adding my save files up haha). I've been noticing over the past month that my thumbsticks are starting to get these little bumps all over them. I tried gently picking at them to see if it was just dirt but they're like a part of the rubber. It is most prevalent on the right stick, which is weird because I don't have any games that even use the right stick except for very light menu stuff. I don't want to pick any more in case I take off the rubber. The left stick is only just starting to develop these bumps, which is weird because I use it for everything EXCEPT menus.

Does anyone know how the sticks are inside? Like, does the rubber go all the way down the stick or is it just a little layer on top that's glued on? I don't want my sticks to be completely ruined. I heard there are some covers you can also get for the sticks - anyone have any experience with certain brands/models?

I wish my sticks had little bumps on them. My left stick has been used so much it has smoothed out and is too slippery now.

@mosespippy: Maybe my Vita has a self defense mechanism against that.

@xyzygy: I'm unsure why this would happen, but I recommend you try using Hori stick covers. They have a wide variety on offer, for a reasonable price too.