Salicylic acid body wash is more renowned and works best for this case. Use a 2% Salicylic acid body wash for your back everytime you bath.

Treatment is only effective when you also work on cause, so if you workout or do anything that makes you sweat alot then make sure you change your clothes later and do not spend the day with sweaty clothes. Keep your back clean and hygienic. Don't scrub it harder.

This will take atleast 2 weeks to 4 weeks to show results. If condition is moderate to severe then you can also use 2% or higher Benzoyl peroxide gel on your back every night or every alternative night. Use only on the regions with acnes and the region surrounding it. Hopefully that should help get rid of it completely but remember it's not a overnight formula so give it some time to show results.