First time playing with my nipples, noticed something on my nipple

It's my first time playing with my nipples and i noticed that the edges of the nipple itself is (i dont know the right description) crusty? or thicker? than the nipple center itself like its dry? Is this something I need to worry about?

For context, I am a work from home person and usually doesnt go out so i always wear shirts without bra and even do walking and cardio without bra too. Could it be just friction? TyTy