After the cup is inserted, it forms a seal with the vaginal wall beneath the cervix, so that menstrual fluid being released through the cervix is collected inside the cup. The outside of the cup will typically be coated in your natural lubrication, making it easier to remove, empty, and re-insert. If the cup is inserted after your period has already started, there may be some blood on the outside of the cup from your flow. If properly inserted and removed, fluid of any kind should be minimal. There is a learning curve for most users, in the beginning, that may require practice to ensure that your cup is properly sealed upon insertion to prevent leaks. You can use a backup liner, pad or period underwear until you get the hang of it.