You may be thinking at this point "but I've never been pregnant or breast fed prior to this leaking". This leaking can occur at any time, pregnant or not, history of breast feeding or not.
During your normal monthly breast self exams, you will see some discharge when you squeeze the nipple. If you start seeing any discharge that occurs without this exam, and have the following, please consult your doctor right away:
Leaking without squeezing
Leaking that occurs often (for those who are not currently breast feeding)
Leaking from one nipple more than the other, or just that one alone.
If the discharge contains any tint of pink or red indicating blood.
If it is clear or solid white in colour
If it appears like egg whites
There may be another cause for those women who see leaking from both nipples. These women have what is known as "galactorrhea". They have a harmless, tiny tumor in the brain that triggers a response for more milk producing hormones called prolactin. This tumor (or even tumors) do not require surgery to remove.
Always discuss any concerns you may have with your doctor. Tell him or her your symptoms, ask for a breast exam or mammogram if necessary. Let your doctor know if you are on any medications prescribed by other physicians. Some medications cause this, so read the pharmacy labels carefully.
Good question, no idea! Try googling it.
I forgot to mention that I don't have any children, so it's not like this is something my body has gone through already.