Black Blood during Periods -7 common causes explained

Key Takeaways:

• Black period blood is usually old blood that took longer to leave your body.
• It’s common at the start or end of your period.
• Colour changes during your cycle are often normal and based on flow, hormones, and timing.
• Infections, PCOS, and stress can also affect blood colour.
• If the blood smells bad, comes with pain, or appears mid-cycle, see a doctor.

Noticed black blood during your period? And you’re feeling a bit worried?

We get it. It can look strange. It’s not what you expect to see and naturally, it makes you pause.

But before you jump to conclusions, take a breath. This change isn’t always a sign that something is wrong.

We’ve seen this question come up again and again among friends, in online forums, and even in doctor’s waiting rooms. That’s why we decided to write this blog.

We want to talk about what black period blood really means. Not all of it is alarming. Some of it is natural. And yes, sometimes, it may need your attention.

We’ll take you through the causes, when to worry, and how to deal with it. Step by step.

Why is my period blood black?

If you’ve spotted black or dark brown blood during your period, don’t panic. It usually means the blood is old. When your flow slows down, especially at the start or end of your period, blood may sit in the uterus or vagina for longer. This delay allows the blood to oxidize, turning it from red to brown or black.

Oxidation is simply a reaction that happens when blood is exposed to air. Just like how a banana turns brown when left out, menstrual blood darkens over time.

According to Healthline, black period blood is often a normal part of your cycle and not usually a cause for concern. But if it comes with a foul smell, itching, or large clots, you may want to talk to your doctor. It’s about knowing what’s usual for your body.

7 common causes of black blood during periods

1. Old Blood Flow
2. End of the Period
3. Delayed Shedding or Light Flow
4. Hormonal Imbalance
5. Birth Control or IUD Effects
6. Infection or STI
7. Miscarriage or Implantation Bleeding

Let’s break down these most common reasons one by one.

1. Old blood flow: When blood stays in your uterus or vagina longer, it turns darker. This happens when the flow is light or slow. Air exposure causes oxidation, which turns red blood to brown or black. It’s usually harmless.
   
   
2. End of the Period: Toward the end of your cycle, the flow slows down. The body clears out leftover blood and tissue. This old blood often comes out looking dark brown or black. It’s your body wrapping things up.
   
   
3. Delayed shedding or Light flow: Some women experience slower uterine shedding. This delay gives blood time to change colour before it exits. You may also see black blood if your flow is naturally light. The slower the exit, the darker it appears.
   
   
4. Hormonal Imbalance: Your hormones control how the uterine lining builds and sheds. If estrogen and progesterone are out of sync, your cycle may slow down. This can delay bleeding, which makes blood look darker. According to the Cleveland Clinic (2024), hormone issues like PCOS or thyroid problems can affect the timing of your period. If your cycles are irregular or change suddenly, get your hormone levels checked.
   
   
5. Birth Control or IUD Effects: Hormonal birth control can thin your uterine lining. That means less bleeding, and often darker discharge. IUDs may also change how your body sheds the lining. Black blood isn’t uncommon, especially during adjustment periods. If it keeps happening or feels off, talk to your doctor.
   
   
6. Infection or STI: Sometimes black blood points to infection. If it smells bad, feels itchy, or comes with pain, don’t ignore it. Infections like bacterial vaginosis or STIs (e.g., gonorrhoea) can affect vaginal discharge. A 2024 update from the CDC warns that untreated STIs can lead to complications. So, if your period blood smells strong or feels wrong, book a test.
   
   
7. Miscarriage or implantation bleeding: Black blood can appear after a very early miscarriage or during implantation. This usually shows up as spotting. You might not even know you were pregnant. If it’s paired with cramping or heavy bleeding, see a doctor. Better to be sure.

Period blood colours and what they mean

Your period blood doesn’t stay the same colour every day, and that’s normal. It changes based on the flow, how long the blood stays in your uterus or vagina, and your overall health.

Here’s what different colours usually mean:

Bright Red Blood

This is fresh blood. You’ll often see it on the first or second day when your flow is at its heaviest.

Dark Red Period blood

This blood has had time to oxidize slightly. It often shows up during sleep or toward the end of your flow.

Brown period blood

This is old blood leaving your body. You might notice it at the beginning or end of your period, and it's usually not a cause for concern.

Pink blood

Pink period blood is often a mix of blood and cervical fluid. It can appear with light flow, spotting, or after exercise. Low estrogen levels may also cause this.

Orange coloured blood

This may happen when blood mixes with cervical fluid or if there's a possible infection. If it’s also foul-smelling or you have itching, talk to a doctor.

What affects the colour?

• Flow speed: Faster flow = brighter red
• Time inside the body: Longer = darker or brown
• Hormone levels: Low estrogen can cause pink discharge
• Infections or STIs: May affect colour and smell
• Diet and exercise: Can cause lighter or delayed bleeding

Remember, your period is a form of communication from your body! Don't doubt your instinct. If it feels off, say something.

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When to contact a doctor?

Most of the time, black blood during your period isn’t serious. It’s often just old blood leaving your body at a slower pace. But some signs need more attention.

If black discharge shows up outside your period, smells foul, or comes with pain or itching, your body may be signalling a problem. This could mean an infection, a hormonal issue, or something that needs a closer look.

Don’t ignore it if:

1. You feel sharp cramps or pelvic pain
2. The blood smells strong or unpleasant
3. You notice itching, burning, or swelling
4. Black discharge appears mid-cycle
5. You see large or frequent clots
6. Your periods suddenly change in pattern or flow

These symptoms don’t always mean something serious. But they’re worth checking.

If you're unsure or feel uncomfortable, talk to a gynaecologist. A simple test or scan can often rule things out quickly.

Final thoughts

Black period blood may look alarming, but in most cases, it’s completely normal. It usually means older blood is taking its time to leave your body.

But if you notice a foul smell, itching, pain, or black discharge mid-cycle, it’s best to talk to a doctor.

We hope you found this blog useful and learned something about what black period blood can mean. If you already have this experience, you are welcome to share your story in the comments, it may help other women too.

Frequently asked questions

Q. What colour is unhealthy period blood?

Unhealthy blood may look grey, bright orange, or greenish. If it smells bad or comes with itching or pain, see a doctor. These signs may point to infection or other issues.

Q. Does black period mean pregnancy?

No, black period blood doesn’t mean you’re pregnant. It usually means the blood is old and took longer to leave your body. It’s common at the start or end of your period.

Q. Can period blood be any colour?

Yes, it can be red, brown, black, pink, or even orange. The colour depends on flow, hormones, and how long blood stays in the body. Most colour changes are normal.

Q. Can PCOS cause black discharge?

Yes, PCOS can delay periods. That delay may cause blood to darken before it leaves your body. It’s not unusual to see black or brown discharge in such cases.

Q. Can stress affect period blood colour?

Yes. Stress can delay ovulation and your period. Delayed periods may cause darker blood, often brown or black.

Q. Is watery period blood normal?

Yes, it can happen. Watery blood often means lighter flow or low iron. But if it lasts long or looks unusual, talk to a doctor.