I want to lighten some of my skin parts like my butt and belly because they are much darker.

Topical application of Melarase creams and Melapads can help lighten pigmentation in the buttocks and in the private areas. The products can be used at home and are safe for use in non-mucosa skin. Best, Dr. Karamanoukian Los Angeles

I suggest a formal consultation with a cosmetic dermatologist who treats pigmentation with lasers ,peels, and lightening skin care.  Best, Dr. Emer.