Why Is Period Blood Sometimes Black? 8 Reasons for Black Period Blood

The colors of menstrual blood can range from bright red to orange, brown, or even black. It’s important to note that black period blood isn’t literally black; it's just so dark that it looks black. While these variations are generally normal, sometimes the appearance of black period blood indicates a problem that could need medical attention.

Causes of black period blood and discharge

Black period blood is blood that takes extra time to leave the uterus, becoming oxidized along the way. When blood is exposed to oxygen, it becomes oxidized and turns dark brown or blackish, similar to the color of coffee grounds.

Black period blood and vaginal discharge isn’t always a cause for concern. It commonly occurs at different times throughout a cycle, particularly toward the beginning of a period.

Vaginal discharge can sometimes give clues about your health. There are multiple possible explanations for black period blood. Here are eight possible causes of black period blood:

1. It’s the beginning (or end) of a period.

Blood flow tends to be slightly slower at the beginning and end of a period (and you can use our online period calculator to predict when that will be, FYI). The longer it takes for blood to leave the body, the more time it has to oxidize and turn into black period blood. 

2. Something could be stuck inside the vagina.

Black period blood sometimes points to the presence of a foreign object in the vagina, such as a forgotten tampon. 

Other objects that might get lodged in the vagina include condoms, sex toys, and contraceptive devices such as sponges, diaphragms, rings, and cervical caps. Over time, these can irritate the vaginal lining and trigger an infection. Aside from black period blood, an infection might cause other symptoms, such as:

• Vaginal discharge with an unpleasant odor
• Discomfort or itching in or around the vagina
• Rash or swelling of the genital area
• Fever
• Difficulty urinating
• Pelvic or abdominal pain

If you notice black period blood in combination with any of the above symptoms and suspect something is stuck inside you, seek help immediately. In rare cases, it could lead to a life-threatening infection known as toxic shock syndrome. 

3. It’s retained period blood.

Retained menses (hematocolpos) is when menstrual blood cannot leave the vaginal canal and fills the vagina, slowly growing darker over time. 

Congenital conditions of the vaginal septum or hymen are frequently responsible for this vaginal blockage. In rare instances, the absence of a cervix (cervical agenesis) or a surgical complication known as cervical atresia can also cause retained menses. Since it’s a rare condition that’s most often caused by congenital abnormalities, this condition is usually diagnosed during adolescence.

When the blockage is severe, it can cause a complete lack of menses (amenorrhea). Other symptoms associated with hematocolpos include a cramping pain in the lower abdomen and adhesions.

4. There’s a possibility of cervical cancer. 

In very rare cases, black period blood, especially when combined with irregular bleeding after sex or between periods, may be a warning sign of cervical cancer.

Early-stage cervical cancer generally doesn’t have signs or symptoms. In more advanced stages of cervical cancer, there may be symptoms such as heavy, watery, bloody vaginal discharge with a foul odor and vaginal bleeding that can eventually turn into dark brown or black period blood. Other telltale signs in the advanced stages of cervical cancer include:

• Fatigue
• Longer or heavier periods
• Pain during sex
• Bleeding during or after sex
• Weight loss
• Pelvic pain
• Difficulty urinating
• Difficulty passing bowel movements
• Swelling in the legs

5. Postpartum lochia has developed.

Normal vaginal bleeding that continues six to eight weeks after childbirth is referred to as lochia. It starts out as a heavy flow that’s reddish in color and contains small blood clots, then slows down after a few days. In the early days, abundant blood can become oxidized and turn so dark that it might seem almost black. 

After a little while, the color gradually lightens, changing to yellow or creamy, before the flow stops altogether. Consult a health care provider if lochia is bright red, contains plum-sized clots, or if there is foul-smelling discharge in the weeks after delivery. 

6. Miscarriage has occurred.

Miscarriage can happen within the first 20 weeks of pregnancy. Dark red spotting, which may be confused with black period blood, can sometimes indicate early miscarriage. Experts estimate that 10 percent of pregnancies end in miscarriage. 

Aside from black period blood, there may not be any other symptoms of miscarriage, such as heavy bleeding or pain. Some people continue to experience the usual signs of pregnancy, a phenomenon known as a missed miscarriage. Detectable only by ultrasound, a missed miscarriage occurs when the embryo stops developing but doesn’t get expelled by the body. 

7. It’s the product of implantation bleeding.

Sometimes implantation bleeding that indicates early conception or pregnancy can be confused with dark brown or black period blood. Dark blood after implantation bleeding is very rare, though.  

Implantation bleeding sometimes appears 10 to 14 days after a fertilized egg implants itself into the uterine lining. The flow lasts for just a couple of days and is usually light, but may become black if it leaves the vagina too slowly. Apart from spotting, other signs of early pregnancy and implantation include swollen and tender breasts and fatigue. 

Implantation bleeding doesn’t occur in all pregnancies. If you do experience implantation bleeding or suspect you may be pregnant, be sure to visit your health care provider.

8. You have a sexually transmitted infection (STI).

Black period blood has been associated with sexually transmitted infections such as chlamydia and gonorrhea. Dark brown or black discharge is occasionally accompanied by other STI symptoms such as:

• Vaginal discharge with an unpleasant odor
• Burning while urinating
• Pain during sex
• Bleeding during or after sex
• Pelvic pressure or pain
• Vaginal itching
• Spotting between periods

Left untreated, STIs can spread and cause pelvic inflammatory disease (PID), which infects the cervix, uterus, and other reproductive organs. PID complications include chronic pelvic pain and infertility.

Lastly, dark brown or black period blood might also indicate other underlying health issues such as endometriosis, uterine fibroids, endometrial polyps, or an ectopic pregnancy.

Black period blood treatment options

If you have any concerns or aren’t sure what’s causing black period blood, make sure to visit a health care provider. Treatment options depend on the cause of black period blood:

• If there is a foreign object stuck in the vagina, symptoms may include fever, pain, and dark discharge. It’s important to visit a health care provider to have the object removed as soon as possible.
• STIs and pelvic inflammatory disease are typically treated with antibiotics. Follow all instructions provided and finish the entire regimen.
• Although missed miscarriages may resolve on their own, most patients require immediate medical assistance. Remedies include prescription drugs or a dilation and curettage procedure to remove remaining tissues from the uterus.
• With retained menses, surgery might be needed to remedy the conditions that initially caused the blockage.
• Cervical cancer is treated with a combination of surgery, chemotherapy, and radiation unique to each patient.

When to see a health care provider

Normal menstrual bleeding lasts two to seven days and occurs about every 21 to 35 days. Black period blood outside of this window may be irregular and needs to be discussed with a health care provider. 

If dark discharge occurs during pregnancy or after delivery, or while entering menopause, it’s important to consult with a health care provider, as it could point to a serious underlying issue. Black period blood accompanied by any of these symptoms also warrants medical attention: 

• Heavy discharge
• Foul-smelling discharge
• Vaginal itching
• Cramping, pain, or fever

Takeaway

Black period blood is sometimes a common monthly occurrence or, in rare cases, a symptom of a larger issue. If you suspect you have any of the conditions outlined above, make an appointment with a health care provider. Treatment of black period blood will be based primarily on what caused it in the first place.