Inquiry regarding buttock discoloration treatment

Hello, I am writing to ask a question because I have concerns regarding hyperpigmentation.

Perhaps because I sit in a chair for a long time, I have developed black discoloration on that part of my buttocks, as shown in the photo. It didn't appear recently; I've had it for a while, but it bothers me every time I see it. I am asking this question to see if there is any treatment I can get at a dermatology clinic. Also, how effective are the creams or ointments recommended by dermatologists? The prices are quite high, so it is difficult to make a decision easily.

I see a lot of ads for discoloration creams in commercials and online stores, but I'm not sure if they are effective. Also, I've been getting boils or pimples in that area, so I'm wondering if that's related to the discoloration.