The breasts are hormonally regulated tissues with the primary function of lactation to feed the young. The breasts undergo tightly regulated developmental cycles throughout life that control the growth of milk ducts, secretion of milk and lactation. Discharge from the nipple can occur from natural changes in the body or as a result of disease.
Pregnant women may experience nipple leakage, as early as week 12 of pregnancy. According to the University of Cincinnati, the breasts begin to generate colostrum early in pregnancy, before the secretion of milk. Colostrum is a fluid rich in antibodies that makes up a component of breast milk.
Colostrum is a thick, sticky substance that can appear milky or yellowish. The colostrum in pregnant women can be secreted manually, and it can leak from the nipple in the last trimester.
Secretion during pregnancy is normal, but if you are concerned about nipple discharge, discuss your concerns with your doctor.
Abnormal discharge from the nipple can be an indication of breast cancer. According to South Dakota State University, between 10 and 15 percent of women with noncancerous breast tumors, and around 3 percent of women with breast cancer, experience abnormal discharge from their nipples. Discharge as a result of a tumor usually occurs in only one breast, and presents as nipple leakage without manual stimulation.
South Dakota State University reports that nipple discharge as a symptom of breast tumors can appear as clear, watery or bloody. If you experience nipple discharge, South Dakota State University recommends leaving the nipple alone, and discussing your secretions with your doctor.
Discharge from the nipple during pregnancy and lactation occurs as a result of hormonal changes over the course of pregnancy. A specific hormone, prolactin, plays a large role in the production and secretion of milk within the breast. Hyperprolactinemia occurs when too much prolactin is secreted from the pituitary gland in the brain, leading to milk production without pregnancy.
According to the University of Washington, hyperprolactinemia may be caused by a type of brain cancer called prolactinoma, a tumor that secretes prolactin. Hyperprolactinemia can also be caused as a side effect of taking other medications, or other hormone imbalances. If you experience milk secretion when you are not pregnant, visit your doctor.