What is the biological difference between vaginal bleeding and your period?

PeriodsR predictable: Normal menstrual periods are cyclical or predictable. The bleeding comes from shedding the lining of the uterus in response to the cyclical change in your hormone levels. Vaginal bleeding (vb) is unpredictable and may be related to various things including trauma, infection, tumors, medications, atrophy, etc. Abnormal vaginal bleeding should be evaluated by your physician.