I find that I get acne on my back more easily than on my face. Since it's on the back, it's hard to reach and out of sight, so I think it's harder to manage.
The first cause of back acne is pajamas. We wear sleepwear a lot in the winter, right? Since sleepwear doesn't absorb sweat and isn't breathable, back acne tends to break out easily. It is definitely different from the summer when you wear cotton t-shirts or thin pajamas.
The second factor is shower products. While shampoo or conditioner can cause back acne, body wash plays a role as well. Switching to soap was the most effective for my back acne. This could be because soap cleans thoroughly, or it could be because body washes contain relatively more harmful ingredients compared to soap.
It might be a bit drying for dry skin types in the winter, but since it's summer, give it a try. It's also great because you can practice zero waste.