What are some home remedies for back acne and back acne scars?

Benzoyl peroxide: The best over the counter acne treatments contain benzoyl peroxide and salicylic acid. They can each be applied once a day. Be careful with the benzoyl peroxide, as it can bleach fabric. If what you are referring to as scarring, is simply redness, or increased pigmentation, then keeping out of the sun will allow it to fade, over time. True scarring, textural changes, are, sadly, permanent.

Some help: Regular use of antibacterial soap helps dry skin & kill off some bacteria residing there. Loofah or scrub brush to help remove dead skin. Sunshine (it's 24f here today) exposure helps some. Astringent ("witch hazel" etc.) can dry & kill bacteria as well. If these don't improve it, will need to see dermatologist for meds.