Lately, in addition to the more intense abdominal pain than usual, my period is manifesting itself in dark brown/black (tarry-like) blood from the start and staying like that for almost 5 days until it finally turns the bright red.

Is this something to be concerned about? Does menstrual blood change in colour during menstruation?

  • I agree about the "basic health concerns in half the population"! I would also hope that someday we get tags for these issues! Good luck on this health concern! Sep 7, 2016 at 21:54
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    Hi @user51778. I have edited your question by deleting some "personal parts" which might be seen as off topic on health SE (and lead to closing of your question). I have provided an answer below, and stayed quite general. If you need a more accurate response (taking into account your personal medical history) I would suggest seeing your gynaecologist. Hope you understand. Best regards. M. Arrowsmith (and actually, the tags you were suggesting were already available so I added them to your question) Sep 7, 2016 at 22:52

1 Answer 1


Menstrual blood is composed of a mixture of blood (blood cells), vaginal secretions, endometrial cells and inflammatory cells.

I have found no study investigating the change in colour of mentruation blood .

However, the presence of endometrial cells (mucosa lining of the uterus) and necrotic cells (from the endometrium) is supposed to be highest during the first days of menstruation where the stratum functionalis gets cleaved from the stratum basalis in the endometrium.

During the end of menstruation most of these cells have been expulsed and the new lining of the endometrial wall has developed, slowly "covering" previous bleeding vessels from the underlying mucosa. This could possibly explain the change in colour you are mentionning.

Some weeks ago, I have answered a question on the menstrual cycle including some points regarding the uterine wall and its changes during the cycle: How does my body know how long a month is?

Of course, these explanations apply to a "physiological" condition, and not to a pathological condition where things can be different.

Sources: Yang H, Zhou B, Prinz M, Siegel D. Proteomic Analysis of Menstrual Blood. Molecular & Cellular Proteomics : MCP. 2012;11(10):1024-1035. doi:10.1074/mcp.M112.018390.

  • Thanks for the answer! So for clarification, it's normal for the darkened colors (even at the beginning)? I knew that the change to dark near the end of the length of the period was normal, but I didn't know whether it was normal to start off being tarry and black like? I didn't know if the the highest amount of enometrial and necrotic cells would be darker or brighter? Sep 8, 2016 at 21:15
  • Hi. At the beginning, the changes in hormonal concentrations (which eventually lead to menstruation) are such, that the constriction of the vessels in the endometrium lead to a great part of the stratum functionalis to be cleaved. That's why the first days contain the highest content. Towards the end, the hormonal concentrations start to change, the new layer has slowly started to form, hence the reduced discharge and the possible change in colour (although this is a very subjective parameter). Note that this concerns "physiological" cases, e.g contraceptive use or IUD may change this. BR Sep 10, 2016 at 8:15

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