A spontaneous nipple discharge not related to lactation or pregnancy is an abnormal finding. It may result from a lesion in the breast (such as papilloma or carcinoma) or from a hormonal abnormality (such as a prolactin-secreting pituitary adenoma). Nipple discharge can be serous (yellow), mucinous (clear and watery), milky, sanguineous (bloody), purulent, multicolored and sticky, or serosanguineous (pink), and the characteristics of the discharge can help in diagnosing the underlying cause.