Everyone’s cycle varies, from the severity of their PMS symptoms to the kind of discharge they expel. During menstruation, the body removes tissue and blood from the uterus via the vagina, which can range in color from bright red to dark brown or black, depending on how old it is. Blood that remains in the uterus for an extended period reacts with oxygen and has had time to oxidize, resulting in a dark appearance.

Hormonal changes and health factors can also influence the color and texture of your menstrual blood. It can be scary to experience sudden changes in your cycle, especially with no explanation as to why. While period blood that has become black usually is not usually cause for concern, it can sometimes indicate a more serious medical issue on rare occasions. Let’s dive deeper.

Meet the Expert: Dr. Diana Rangaves writes for 21Ninety’s as a health and wellness expert. She is a pharmacist, philanthropist, and ethics professor turned writer, holding a Doctorate in Pharmacy from the University of California. She also serves as the Executive Editor and Chief Content Officer for Healthcare Worldwide Central and has published several works in medical and pharmaceutical publications, academic books, as well as, scholarly articles.

Potential Causes of Black Menstruation Blood

One of the most prevalent causes of black period blood is menstrual blood that has been left in the uterus for an extended period. Menstrual blood is typically red or brown because of the presence of oxygen, which causes the blood to oxidize. However, when blood is held in the uterus for an extended period, the lack of oxygen causes the blood to become black. This can happen if you have a light flow or your cervix is closed during your period.

Black menstrual blood and vaginal discharge are not necessarily cause for alarm. It frequently occurs at various points throughout a cycle, notably at the start or end of a period. The vaginal discharge might occasionally provide signs about your health. There are several plausible explanations for black period blood. Here are some possibilities to consider:

Hormonal Imbalance

Black period blood can also result from hormonal abnormalities. Hormones like progesterone and estrogen primarily regulate your menstrual cycle. Unbalanced levels of these hormones can alter the thickness of your uterine lining, which can result in irregular menstruation and unusual bleeding. The blood may also appear dark brown or black due to this.

An Object Stuck in the Vagina

Period blood may indicate the presence of an object or foreign body in the vagina, such as a tampon that was left behind. Other items that could become lodged in the vagina are sex toys, condoms, and contraceptive devices such as cervical caps, rings, sponges, and diaphragms.

These have the potential to irritate and infect the vaginal lining over time. In addition to black period blood, other signs of an infection could include:

  • Vaginal discharge with an unpleasant odor
  • Itching or discomfort in the vaginal area
  • Swelling or rash in the vaginal region
  • Fever
  • Having trouble urinating
  • Pain in the abdomen or pelvis

Seek medical attention right away if you have any of the above symptoms along with black period blood and suspect something is lodged inside of you.


Black period blood can also result from illnesses, including bacterial vaginosis and sexually transmitted infections (STIs). These infections have the potential to irritate and inflame the uterus and cervix, which can result in irregular discharge and bleeding. It’s crucial to go over treatment choices with your healthcare professional if you think you could have an infection.

Polyps or Fibroids

Growths in the uterus called fibroids and polyps can result in irregular bleeding and discomfort. Fibroids are substantial, bigger growths that can form inside or outside the uterus, whereas polyps are tiny, non-cancerous growths that form on the uterus lining. Black or dark brown period blood, along with additional symptoms, including severe bleeding and cramping, can be caused by either of these illnesses.


The disease known as endometriosis is a condition where the tissue that usually lines the uterus grows outside of it, leading to pain and irregular bleeding. Along with other symptoms like cramps, back discomfort, and heavy bleeding, women who have endometriosis may experience black or dark brown period blood. It’s crucial to discuss treatment options with your healthcare professional if you think you might have endometriosis.

A Risk of Cervical Cancer

In extremely rare situations, black period blood, especially when accompanied by irregular bleeding after sex or between periods, may indicate cervical cancer. Cervical cancer, in its early stages, usually shows no signs or symptoms. In the later stages of cervical cancer, symptoms may include heavy, watery, bloody vaginal discharge with a foul odor, as well as vaginal bleeding that can progress to dark brown or black menstrual blood.

Other warning signals in the advanced stages of cervical cancer include:

  • Fatigue
  • Longer or heavier periods.
  • Pain During Sex
  • Bleeding during or after sex
  • Weight loss.
  • Pelvic discomfort.
  • Urinary difficulties.
  • Difficulty passing stool
  • Swelling in the legs.

Retained Period Blood

Retained menstruation (hematocolpos) occurs when menstrual blood is unable to leave the vaginal canal and fills it, gradually darkening over time. Congenital problems with the vaginal septum or hymen typically cause this vaginal obstruction. In rare cases, the absence of a cervix (cervical agenesis) or a surgical condition known as cervical atresia can induce retained menstruation.

Because it is an uncommon disorder caused primarily by congenital disabilities, it is typically identified in adolescence. A severe obstruction can result in a complete lack of menstruation (amenorrhea). Other symptoms of hematocolpos include cramping pain and adhesions in the lower abdomen.


Throughout the first 20 weeks of pregnancy, miscarriage is possible. Sometimes, dark red spotting—which can be mistaken for black menstrual blood—might be a sign of an early miscarriage. There might not be any other signs of a miscarriage, such as severe bleeding or pain, except from dark period blood. A condition known as a missed miscarriage occurs when a person still exhibits the typical symptoms of pregnancy. A missed miscarriage is identified solely by ultrasound; it happens when the embryo ceases to develop but is not eliminated by the body.

When To Seek Medical Attention

Black period blood can happen for various causes, and it is not unusual. You may make more informed decisions about your menstrual cycle health if you are aware of the underlying causes. Do not hesitate to consult your healthcare professional if you have any unexpected symptoms or questions regarding your menstrual period. Remember that every woman has a different menstrual cycle, and variations in the color, texture, or flow are common.