OK, I'm new to the sculpting aspect of 3D modeling and have run into this problem multiple time and don't know how to solve it.
While sculpting I manage to overlap area of the mesh (mainly because I am not paying attention). Using the deflate or smooth brush seems to make it worse.
Smooth, reduce, flatten, smooth reduce ..... if your in Symmetry mode .. Hit (9) on your keyboard, it will disappear half so you can work from the inside. The problem with Sculptris, the brush tool only works on the Normal ... not on backfaces, when the mesh crosses the backfaces start showing through. You can also Hide (H+Drag box) parts so you can work from inside .. hope this helps