Hi, You have not mentioned your age, and is it in one nipple or both ?
We are mentioning the commonest cause for Nipple Discharge
, which is Mammary Duct Ectasia. In this one or more of the ducts beneath your nipple becomes inflamed and clogged with a thick, sticky, green or black substance. Some of your symptoms can be relieved by applying warm compresses to your breast. Over the counter Analgesics can help reduce the pain. Never the less Nipple discharge should be thoroughly investigated. We suggest you to get completely evaluated by a doctor.