Dark brown blood between periods is almost always harmless and can be a result of ovulation, blood leftover from a period, pregnancy or stress. What to Expect suggests keeping a journal to track a period and any additional bleeding between periods in order to help determine the cause of any unexpected bleeding.
Dark brown bleeding that takes place a few days after a period ends is the most common is most likely to be leftover blood being expelled from the uterus, according to What to Expect. This is a completely normal process and requires little more than a sanitary napkin for a day or two to protect clothing.
Bleeding directly in between periods can signify ovulation; this blood ranges from dark brown to red. Implantation bleeding, which is light bleeding that occurs shortly after becoming pregnant, can also be a dark brown color. Stress can also cause changes in the menstrual flow that lead to breakthrough bleeding between periods, according to Everyday Health.
While light bleeding between periods is in most cases normal, if the dark brown blood turns bright red, is accompanied by cramping or lasts for more than three days, it is important to contact a doctor to determine a cause, according to Everyday Health. The New York Times suggests inserting a tampon to confirm that any bleeding is indeed coming from the vagina. According to Healthline, in very rare cases, brown blood can indicate uterine cancer.