What is the cause of a sticky nipple discharge?

Nipple discharge: Nipple discharge that is transparent or sticky should be evaluated by your doctor. Clear and sticky discharge is very much like plasma, since that is the source of the secretion. Unilateral spontaneous clear or bloody discharge is considered suspicious and requires a full workup.

Not sure: Reasons for nipple discharge can include stimulation of the breast, pregnancy, medications, galactorrhea (secretion of milk or similar substance), an abscess or other breast infection, hormonal imbalances (like hypothyroidism), fibrocystic breasts (breasts are very fibrous), blocked mammary duct, breast cancer and intraductal papilloma (non cancerous mass), use of marijuana, anise and fennel.