What's the deal with the pulls on my clothing?

I don’t really know how else to describe it… my clothing, everything from white Hanes T-shirts to American Apparel shirts, to some of my hoodies, have balls of material developing on them.

Is this from the washing machines in my building? Dryers? Am I doing something wrong? At first I thought it was just the material of a shirt or two, but now I realize it’s happening on a wide variety of clothing. Advice?