Brown or dark period blood often indicates that the body is expelling old blood, says MDhealth.com. Sometimes, blood remains in the uterine folds and is released later during the menstrual cycle, usually at the end. Old blood ranges in color from dark red to brown or black.
Brown blood is generally nothing to worry about because it is a completely natural occurrence, according to Lady Care Health. However, if the discharge is accompanied by other troublesome symptoms, such as severe pain, a strange or foul odor, or prolonged bleeding, a medical examination may be necessary to rule out any underlying medical conditions.