The development of male nipples may be caused by the following conditions: 1. It may be due to abnormal secretion of sex hormones during puberty, i.e., the secretion of more estrogen than androgens, and the sensitivity of the breasts to estrogen, resulting in the development of male breasts, especially in men with better development. 2. The development of the nucleus pulposus usually occurs unilaterally, mostly due to the sensitivity of the cells of the nipple to estrogen. The causes of male nipple protrusion are complex, and if accompanied by other abnormal symptoms, it is recommended to go to the relevant hospital department for further examination and if necessary, treatment.