Why do women's breast/nipples hurt during their menstrual cycle?

Why do women's breast/nipples hurt during their menstrual cycle?
Hormonal surges during certain times in your menstrual cycle cause breast tenderness and sensitivity. Taking oral birth control can make this worse. It's painful, but normal.
It has to do with changing hormone levels. My breast get tender, sore and itch. They also get firmer and it seems like they are a little bigger.
Its all to do with the hormone changes- our hormones fluctuate crazily during menstrual cycles- Elevated levels of oestrogen is to blame for all the known symptoms of PMS.