Overall health conditions are more likely to affect the timing and length of your period than it's appearance—but there are some reasons why your period blood may vary in color.
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. So, what do the different hues mean?
Nothing that medically relevant.
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 period is not just a pool of old blood waiting to escape.
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.
When you get your period, these specialized spiral arteries constrict, and actually limit blood flow loss (1). So, even though it may look like fresh red wound blood is pouring out of your vagina, rest assured, there is no wound that you are bleeding from. 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.
Here’s what’s going on with the different colors:
Brown/dark red period 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 fluid-y. If your period blood appears brownish at the start or end, 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 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.
Bleeding that mixes with fertile cervical fluid can appear light red or pinkish according to some people.
Gray: If you have grayish discharge, talk to your doctor as this can be the sign of an infection or a miscarriage.
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 in period blood color is normal, and doesn’t signify anything serious.
Understand what’s going on in your body. Download Clue and learn about your own cycle.
- Cunningham FG, Leveno KJ, Bloom SL, Spong CY, Dashe JS, Hoffman BL, Casey BM, Sheffield JS. Williams Obstetrics. 24th ed. New York: McGraw Hill Education; 2014. 84–86 p.
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