Itchy skin between my boobs?

Ok so for the past few days my skin between and underneath my boobs has been very dry and itchy. I thought if I used a gentle, light moisturizer and tried to let my boobs “air out” (I work out a lot so I figured maybe they needed a break from being cramped in a sweaty sports bra) then maybe that would help. It’s been awhile though and it hasn’t helped that much. My skin has started to change it texture a bit, become darker a bit leathery.

The picture isn’t one of my own chest, by the way. I found it on google images and it’s extremely similar to how mine looks right now. Any ideas on what this is? Is it serious?