What Causes Flare Up Of Red Itchy Rash On The Surgical Scar Post Mastectomy?

I had breast reconstruction 8 years ago after having a mastectomy 25 years prior to that. Tissue was taken from my stomach and a new breast was made from it and attached to where my previous breast had been. Though the breast is a little larger and heavier than the other side, it has also developed a red line wherever the incisions were made. They become very red on occasion and it appears that a rash is evident. It is itchy and red. With cortisone it does disappear to a faint pink and is not itchy until it flares up again. I have called my surgeon who is out of state and he says he never heard of this before. I am very allergenic and wonder if I could be having a reaction to my skin that is the one from my stomach attached to my chest?