What Causes Dry Skin On Hands And Feet?

ok, the skin on my hands (palms) and feet are extremely dry, which causes me to scratch my palms or the bottom of my feet almost to the point of bleeding. I use A & D ointment which seems to be the one lotion that provides the most relief. My heels crack which also cause my feet to hurt when I walk. I have always regularly used lotion on a daily basis, drink plenty of water, exercise and eat right, what could be causing this. By the way, I first became aware of this extreme dryness to my skin this past summer (June 2014). Is there anything that you may recommend? Thank you!