The human nipple area is rich in nerves, when stimulated by cold or encounter can make yourself feel more excited, the body secretion of hormones will be suddenly increased, will cause the nipple bulge. If you usually like to wear tight clothes or rough clothing, these clothes will constantly stimulate the nipples, which will cause the skin of the nipple area to become more sensitive over time, and will often stimulate the nipples to bulge up on their own. If the skin of the nipple is infected with bacteria or fungus, the bacteria will continue to invade the surrounding ducts along the nipple, resulting in the formation of an inflammatory mass inside the breast and a raised nipple due to redness and swelling. In early stages of papilloma or breast cancer, the nipple may also bulge due to hormonal disruption in the body.