TMI- Rash Between Breasts

Megan
Hi! I've had this rash thing between my breasts forever, and I'm assuming it has something to do with heat/moisture. It has never itched or anything; it's just discoloration. It's more pink when I'm hot and a light brown when I'm cold. It's been there for literally years. Does anyone know what it is? And how to get rid of it?