Sign in to your account

Don't have an account?

Create an account
This website uses cookies to ensure you get the best experience on our website. Learn more
Black medical doctor in a white coat and red stethoscope examining a patient on a ward. Our doctors on askawayhealth have years of clinical experience to provide top notch care.

Need to check your symptoms?

Use our symptom checker to help determine what your symptoms are and to ensure you get the help you need.

Check your symptoms


Request a reset

Don't have an account?

Create an account


Reset your password

Don't have an account?

Create an account


8 Reasons For Passing Black Period Blood – #6 Should Alarm You.

November 1, 2023

You may pass very dark menstrual or even black period blood – should you worry when that happens?

In this post, we analyse the causes of passing black blood during your menstrual periods.

There may be some cases when it’s a natural event, but we share a few causes that can be of concern.

Menstrual blood, or the vaginal bleeding during your period, is typically red.

However, you may find different grades of red, pink, brown or even black during your period. 

They may be the normal blood flow or may indicate some health conditions.

Light red or pink blood may happen during the early part or towards the end of your period. It may also be what you see early after having a baby, called lochia. 

As you get into the later part of the period, it is rich blood red, and sometimes, as it passes out and mixes with air, it may turn a little brown or darker. Brownish blood may also suggest an infection.

But when you get extremely dark or black blood, there could be a fair number of reasons.

Let’s break them down into normal and abnormal reasons.

Normal Reasons for “Why is My Period Blood Black and Thick?”

The first normal reason you could have for your period blood to appear black is the menstrual flow rate (1).

If the blood flow is slow – as it happens towards the beginning and the end of the period, the blood can darken simply because it is pooled in the womb before it emerges in the vagina.

The usual period flow track is a slow start and builds up to a more rapid flow after the first day or so of the period and continues for a few days.

The heavy flow gradually slows down as you approach the end of the period. 

The other thing that can happen in the context of a normal period is that as the blood emerges and is exposed to air, it is oxidised (2), which darkens its colour.

This is similar to when the cut half of an apple or avocado is exposed to air and turns darker.

Oxygen mixes with blood in a natural reaction called oxidation. It explains why your period blood looks darker and sometimes black. 

In addition, black blood may be a feature of some menstrual products – tampons especially (3).

This does not mean that tampons cause black blood, but the way the blood appears on the tampon gives the impression of looking darker.

Blood absorbed unto the tampion gets oxidised slower than that which is not. When you withdraw the tampon, you perceive blood that looks much darker than usual.

Secondly, menstrual blood sometimes contains clots, small fleshy bits of tissue made up of congealed blood.

This is natural and often harmless in small amounts, but it can appear darker than the rest of the menstrual blood when absorbed by the tampon. 

So, while tampons themselves don’t cause the blood to change colour, the way blood interacts with them and the fact that they may absorb and isolate clots can make the blood on a tampon appear darker than it actually is. 

So these are natural reasons you may experience dark or black blood during your periods. It shouldn’t be in large quantities; usually, there are no associated features like pain or other irregularities.

Image showing sanitary towels and a tampon with different degrees of bleeding including black period blood

Abnormal Reasons You May Have Black Period Blood

Now, what about when there is an abnormal process or condition?

Yes, a few conditions could lead to expelling black blood during your periods.

The first is from hormone imbalance (4).

Hormone imbalance is important for regulating the menstrual cycle.

Usually, the womb lining thickens at the beginning of a cycle as it prepares for a possible pregnancy. 

If you don’t get pregnant in that cycle, your hormone levels drop, leading to shedding menstrual blood.

However, suppose there is a hormone imbalance (as occurs in some conditions like PCOS or some thyroid conditions). In that case, the timing of your flow and its intensity can be affected.

If the hormone changes make the womb lining shed more slowly, it can lead to the appearance of black menstrual blood because it has had more time to oxidise.

Changes in the Structure of the Womb

Next are conditions like Fibroids or Endometriosis (5). Fibroids are noncancerous growths in the womb, while endometriosis involves tissue similar to the womb lining growing outside it. Both conditions can cause heavier and more prolonged menstrual bleeding. 

When blood flows slowly or pools in the womb due to these conditions, it can oxidise over time. 

This oxidation process (akin to how an apple turns brown when exposed to air) can make the menstrual blood appear dark, almost black.

Infection within the reproductive tract (6) is another reason for experiencing dark or black menstrual bleeding.

These can be infections (often sexually transmitted) within the womb (endometritis), cervix (cervicitis), or PID (Pelvic Inflammatory Disease), which lead to abnormal discharge and bleeding irregularity, including dark or black blood.

Experiencing symptoms of infection such as pelvic pain, smelly or offensive period/discharge, fever, and other signs of being unwell can indicate these types of infection.

How Drugs May Lead to Black In Period Blood

Next, we have some drugs/medications that could affect the appearance of your menstrual blood. Anticoagulants or blood thinners (7) treat conditions like blood clots (DVT) or abnormal heart rhythms like Atrial Fibrillation.

Blood thinners reduce the blood’s ability to clot. 

When you’re menstruating, the body typically releases natural substances known as clotting factors to help control bleeding and clotting. 

However, these substances may not function as effectively when taking blood thinners. 

It may mean a longer period before the blood is expelled from the womb, allowing it to darken and appear black. So, the slower flow of menstrual blood can result in its colour change.

And the final condition we’re looking at in this video that may be associated with passing what appears like dark or black blood is with or following a miscarriage or some other pregnancy complications (8). 

With miscarriage, for instance, there is vaginal bleeding.

But in addition to blood, foetal tissue may also come away from the womb.

As it can happen at different flow rates, you may have a mixture of fresh red, dark brown or black blood as the blood and tissue break down and oxidise.

You can see why monitoring changes in your period blood is essential. 

For most of us, black period blood in small amounts could happen naturally for the reasons described above.

However, suppose it is associated with symptoms of infection, features of hormone imbalance, happens in large, prolonged amounts, or you consistently experience very dark or black menstrual blood. 

In that case, seeing your doctor to identify the causes and get the right treatments is important.

Let us know about any experiences below – you can reach our doctors here.

More Reading

Editing by AskAwayHealth Team


All AskAwayHealth articles are written by practising Medical Practitioners to help promote quality healthcare. 

The advice in our material does not replace a qualified healthcare practitioner’s management of your specific condition.
Please get in touch with a health practitioner
 to discuss your condition, or reach us directly here.

Our post may contain affiliate links at no cost to you. There is no obligation to use these links. Thank you for being so supportive!

Image Credits: Canva

Share this blog article

On this page

Let us know what you think

Want to know how your comment data is processed? Learn more

Access over 600 resources & our monthly newsletter.

Askawayhealth 2023 grant recipient from European Union Development Fund

Askawayhealth, 2023 Award Recipient

Our educational content meets the standards set by the NHS in their Standard for Creating Health Content guidance.

Askawayhealth aims to deliver reliable and evidence based women's health, family health and sexual health information in a way that is easily relatable and easy for everyone to access.

Askawayhealth symptom Checker tool image

Utilize our complimentary symptom checker tool to gain more information about any uncertain symptoms you might have.