Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. As per your query, you have symptoms of hyper-pigmentation on buttocks, which occur because skin has increased sensitivity of getting pigmented due to acid content and volatile vapors in bleach cream. Need not to worry. I would suggest you to wash area with cold water and body wash containing salicylic acid twice a day. Apply Clindamycin gel at night time. You should drink plenty of fluids and apply cold compresses. If condition doesn t get well in a week then consult dermatologist for proper examination and treatment. Doctor may prescribe antibiotics like Minocycline, steroid ointment and may recommend chemical peeling for marks. Hope I have answered your query. Let me know if I can assist you further.