Some women often experience hardened nipples. This happens because the nerves in the nipple are able to react to stimulation, both physically and psychologically. Some causes that can make your nipples harden, including exciting thoughts, changes in temperature, or cloth on your clothes that rub against the nipples. Both women and men have breasts, and in the breast there are mammary glands. However, only the mammary glands in women can produce milk for baby food sources. Everyone's breast size is different. In fact, usually the size of the right and left breast in a person is also different. Similarly, the size and sensitivity of the nipple. One nipple can be larger than the other nipple. And some people can have nipples that are more sensitive, or less sensitive than most. Causes of hard nipples Sometimes, women experience problems in their breasts, especially in the nipples. The nipple is the area in the middle of the areola (the brown part), which has a hole in the center