“What body wash is good for back acne?”

Try PanOxyl 10% cleanser!

Acne is not treated by any washes, since acne is a genetic condition and NOT caused by dirt. So super scrubbing of the skin will do little for acne, but make the skin overly dry and then too rough, dry, irritated to withstand strong acne medications, which are usually necessary to treat back acne (which is typically tougher to treat than facial acne).