When one or both breasts produce milk or milky discharge and there is no potential for the woman to be pregnant, it is because she suffers from galactorrhea.
A diagnosis for this condition is made when the breasts leak either when touched or on their own. Sometimes, this liquid is yellow or greenish. In any case, it is important to see a specialist to examine why milk is being secreted and determine what is happening.
Other symptoms related to this disease include: not having a period, having irregular periods, headaches, vision loss, a decreased sex drive, an increase in hair growth on the chin or chest, acne and erectile dysfunction in men (galactorrhea can also occur in men, although to a lesser extent).
According to the webpage FamilyDoctor.org, other causes of this condition include: birth control pills, over-stimulation of the breasts, frequent breast self-exams, using irritating clothing, blood pressure medications, sedatives, herbal supplements, psychoactive drugs, kidney disease, an underactive thyroid, an injury or trauma to the chest or spinal cord, and a tumor or defect in the pituitary gland (the pituitary gland is responsible for stimulating the hormones that the gonads and ovulation produce).
Your physician will order blood tests to check your hormone levels, a pregnancy test and, if a tumor is suspected, request an MRI (magnetic resonance imaging).
Related article: Ovulation and pregnancy: common myths (article in Spanish)