Its where all the tiny blood vessels squeeze for some reason (slowing the blood flow), I think sometimes it's hormonal, sometimes it's stress...I've heard of it when it affects breastfeeding but I think you can have it in other areas too. One of my friend's mothers had a similar thing, whenever she touched anything cold she got really irritated, itchy and sore...it's too long ago now so I can't remember what the treatment was.