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Photo by Clár McWeeney

Cycle A-Z

Period blood color: brown, black, or dark — does it matter?

by Clár McWeeney, Former Content Manager at Clue Reviewed by Laurie Ray, Science Writer at Clue
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Top things to know about period blood color

  • Changes in period blood color are normal

  • Dark red, brown or black period blood is simply blood that has reacted with oxygen.

  • Talk to your healthcare provider if you have grayish or pink watery discharge, as this can be a sign of an infection or something more serious like cancer.

You may notice the color of your period blood varies. Sometimes it’s a bit brown, or almost black, to later turn to bright crimson.

Overall health conditions are more likely to affect the timing and length of your period than its appearance—but there are some reasons why your period blood may vary in color.

What does period blood color mean?

Blood (and tissue) changes color depending on how long it has been exposed to air oxygenation. Think of when you cut your skin—red blood comes out of a fresh wound. If you put a bandage on it and check it the next day, you’ll see that once-red blood will have turned brown. Blood color appears darker because it has reacted with oxygen, and the majority of the water in blood will have evaporated, making a more concentrated pigmentation.

Your endometrium is the inner lining of your uterus, which is where a fertilized egg would implant and grow. The endometrium is made up of highly vascularized tissue with special spiralized arteries (1). This provides a fertilized egg with quick and easy access to a fresh blood supply (carrying nutrients and oxygen), so it can start to develop.

Right before you get your period, these specialized spiral arteries constrict, to limit blood loss (1,2). After the constriction of the spiral arteries, the endometrium starts to break away in pieces from the deeper layers of the uterus (3). Your endometrium does not separate all at once, it’s a slower, controlled separation, and it takes time for your endometrial tissue to make its way down through your cervix and vagina. This initial blood and tissue may appear dark red or brown, or even black because it takes longer to exit your body.

As tissue breaks away, it leaves torn ends of blood vessels that continue to bleed (3,4). This is where the bright red blood you may see during your period comes from. Eventually platelets (pieces of cells involved in blood clotting) are activated to group together and form a plug to stop the bleeding, bringing the period to an end (2).

As bleeding slows toward the end of a period, it may once again appear darker red or brown.

A hand holding a phone with the Clue app opened

Understand what’s going on in your body. Track your period in Clue to learn about your menstrual cycle.

Black, brown, or dark red period blood color

At the beginning or end of your period, blood can be a dark brown/red shade and can have a thick consistency—but it’s also normal for the first signs of your period to be bright red and more liquid.

If you notice brown period blood at the start or end of your period, it’s because the blood is older and took longer to leave your uterus. The uterine lining darkens the longer it takes to leave the body.

Period blood clots are normal on the heaviest days of your period, and can appear deep red or almost dark black as well.

Bright red period blood color

Period flow typically becomes heavier on the second or third day of the cycle as the uterine lining sheds faster. Bright red period blood is newer blood, thus it doesn’t have time to darken before it exits your body.

Pink period blood color

Spotting is any bleeding that happens outside of your regular period. Some people experience spotting mid-cycle, also known as ovulation bleeding (4,5). Bleeding that mixes with fertile cervical fluid can appear light red or pinkish.

Watery, pink vaginal discharge that occurs irregularly (without a pattern and not related to your menstrual cycle) may be a sign of cervical cancer and should be evaluated by a healthcare provider (6).

Gray period blood color

If you have grayish discharge, this could be a sign of an infection. If you experience heavy bleeding with pieces of grayish tissue, this could be a sign of a miscarriage. Seeing a healthcare provider is a recommended for either situation.

The significance of period blood color is commonly misunderstood.

One company even raised thousands of dollars on Kickstarter to build a “smart menstrual cup” which would analyze menstrual fluid color.

Reproductive and menstrual health is still gravely misunderstood, and pushed aside compared to other aspects of health. The lack of proper education and research on aspects of female health negatively impacts people globally in so many ways.

A range of period blood colors is normal, and doesn’t signify anything serious.

Changes in the color of your period blood are not anything to worry about. But do pay attention to your flow volume, changes in cycle length, and pain, or any bleeding that doesn’t have a pattern, as these can indicate underlying conditions.

Article was originally published on Oct. 19, 2017.