I got 5 sessions of chemical peel on buttocks for acne scars/dark skin but no results.

Your discoloration may be deep. I would use Luminase and Exfolase body brightening creams followed by fractional laser. Best, Dr. Karamanoukian#Realself100 Surgeon

Buttock skin is very sensitive and healing is unpredictable. Risks of hyperpigmentation are higher as the skin of buttock does not regenerate like face. The key is to perform mild peels for long period of time and use topical creams on a daily basis. If there is continuing active acne the result may not be visible due to new scar formation. Fractionated CO2 laser in mild settings for longer period of time may be an alternative.