Skin issue ?

Mel
So I've been having this for a few years it's below my breasts, under my arms and on my neck and thought it was just dirt I could scrub away but realized that it was just spreading over time. Has anyone ever had this ? If so any suggestions to get rid of it ? (Yes I know I should probably go to the doctor but I'm thinking maybe there's a simple way to get rid of it that I never knew of lol)