I am sure the sensitivity in them plays a part. I only pump and bottle feed and they just always hurt. I use lanolin after every pump session. Even rubbing that on them hurts. When it is cold and my nipples harden it feels like hell. When I take showers, I have to face away from the shower because of the pain. I can't dry them with a towel because that just feels like I am scraping them with needles. Eventually I am going to switch over to formula. But til I do, I want to keep on til I just can't anymore. I just can't imagine that everyone else who breastfeeds and pumps for a long amount of time has this same pain. Just the nipples, not the breasts.