Do you notice if it happens more during one season (like the winter) than others? If it happens more during the winter, I just read in one of my magazines that our girls can get dry and itchy because we wear clothes that don't let them breath as well during the winter as during the summer. You might consider the bras you wear as sometimes the fabric is less breathable. If you don't wear cotton bras, try getting a few of them and see if the problem resolves. Make sure the bra is very supportive to sort of keep your girls up. I don't have that problem because I am not as endowed! But, during the winter, my nipples get itchy. Actually, since I have been using Dove CreamOil Body Wash, they aren't itchy anymore because they are properly hydrated like the rest of my skin.

Bacteria can grow under your girls and between your cleavage if there is alot of moisture from sweat throughout the day. You might consider going into the bathroom once or twice a day and just dry them off with a paper towl to see if that is what is happening as bacteria thrives in moisture.

Otherwise, I would visit a dermatologist or your OBGYN to make sure that there is not underlying problem.