I Have On My Sternum Area And My Neck Very

i have on my sternum area and my neck very dark discoloration and on my sternum area, thick what seems like dead skin layers . has been there for greater than 7years now, sometimes, it fade a little but comes back.i am not sure what it is or how to get rid of it. outskirts of it is redish but the core of it is dark. it is not painful,