Understanding Black Period Blood: 10 Common Causes Explained

Have you ever looked down at your period product and wondered, "Why is my period blood black?" Don’t worry — you’re not alone. While a bright red flow is typical, it’s not uncommon for your period to appear darker, even black at times. This can understandably raise questions, but there’s usually no need to panic — it’s a common, often misunderstood menstrual occurrence.

When blood remains in the uterus longer than usual, it interacts with oxygen, causing it to darken. This oxidised blood is perfectly normal and often shows up toward the end of your period.

That said, if you consistently notice black blood during your period alongside other symptoms like heavy bleeding, intense cramping, or an unpleasant odour, there may be other underlying reasons.

Let’s take a closer look at black menstrual blood and the ten possible causes behind it.

READ: Heavy Bleeding: When to See a Doctor?

What Does Black Blood During Periods Mean?

It’s normal for period blood to vary in colour throughout your menstrual cycle. Black blood typically appears at the beginning or end of your period, when your flow is lighter. This is often due to a natural process called oxidation — when oxygen interacts with the haemoglobin and iron in your blood, causing it to darken. It’s similar to how a sliced apple gradually turns brown when exposed to air.

Black or brownish-black blood is usually nothing to worry about, especially if it appears in small amounts. However, if you experience heavy black bleeding during your period or if it lasts longer than your usual cycle, it’s a good idea to speak with a doctor. Sometimes, it could signal an underlying condition such as hormonal imbalances or uterine fibroids.

What Causes Black Blood During Your Period?

Here are ten possible causes of black blood during menstruation:

1. Start or End of the Period

During your period, the flow changes speed. It can be lighter and slower at the start and end, and the blood may appear dark brown or black rather than bright red. This is because the blood has spent more time in your uterus before exiting your body. The longer it stays, the darker it may become.

Black spotting before your period could also be leftover blood from your previous cycle. This is usually harmless and just your body’s way of clearing out old blood.

2. Foreign Object in the Vagina

In some cases, black discharge instead of fresh blood may indicate a retained foreign object, such as a tampon, condom, sex toy, or contraceptive device (like a sponge, diaphragm, ring, or cervical cap). Over time, these can irritate the vaginal lining and lead to infection.

In addition to dark blood during menstruation, you may experience:

• Foul-smelling vaginal discharge
• Itching or discomfort in the vaginal area
• Rash or swelling near the vagina
• Painful urination
• Pelvic or abdominal pain
• Fever

If you suspect something is lodged in your vagina or have any of these symptoms, see a doctor immediately. In rare cases, it could lead to toxic shock syndrome (TSS) — a life-threatening condition.

3. Sexually Transmitted Infections (STIs)

Black blood during menstruation can also be linked to STIs such as chlamydia or gonorrhoea. Other symptoms may include:

• Foul-smelling discharge
• Burning sensation while urinating
• Pelvic pain or pressure
• Vaginal itching
• Pain or bleeding during sex
• Spotting between periods

STIs are serious infections that require prompt medical attention. If left untreated, they can spread to other parts of the reproductive system. One major complication is pelvic inflammatory disease (PID), which occurs when an untreated STI spreads from the vagina to the cervix, uterus, and other reproductive organs.

Although PID shares many symptoms with STIs, it may also present additional warning signs, such as fever, chills, or unusually painful or heavy periods. If untreated, PID can lead to severe complications like chronic pelvic pain, ectopic pregnancy, and infertility.

READ: Pelvic Inflammatory Disease

4. Menstrual Retention (Hematocolpos)

Menstrual retention, also known as hematocolpos, occurs when menstrual blood can't flow out of the vagina and accumulates inside. This accumulated blood can darken over time, causing discomfort and potential complications. Causes may include:

• Congenital abnormalities, such as an imperforate hymen or vaginal septum, can block the flow of menstrual blood.
• Rare medical conditions like cervical agenesis (absence of the cervix) or cervical atresia (cervical blockage due to surgery) can also cause the condition.

Symptoms include:

• Lower abdominal cramping
• Adhesions (scar tissue) in the vagina
• Endometriosis
• Amenorrhoea (absence of periods)

5. Endometriosis or Adenomyosis

Endometriosis and adenomyosis, characterised by the abnormal growth of endometrial tissue, are two conditions that affect the uterus and menstrual health. They may be associated with:

• Persistent pelvic pain
• Dark, coffee ground-like discharge
• Spotting between periods
• Bleeding lasting longer than seven days

If you experience any of these signs or symptoms, consult your doctor as they can perform tests to diagnose endometriosis or adenomyosis and help manage the condition.

6. Implantation Bleeding

Implantation bleeding occurs when a fertilised egg attaches to the uterine lining, typically 10-14 days after conception. This process may cause a light flow of blood, which can appear black if it exits the body later due to oxidation.

If you're pregnant, you might notice dark brown to brownish-black discharge during or shortly after implantation bleeding. While this is usually harmless, it's important to consult your doctor if the discharge is heavy or accompanied by symptoms like cramps, abdominal pain, or fever, to rule out any complications.

READ: What Should You Know About Implantation Bleeding?

7. Missed Miscarriage

While black spotting and bleeding can occur during a healthy pregnancy, they can also be a sign of a missed miscarriage. This type of miscarriage occurs when the embryo stops developing but remains in the womb without getting expelled.

Missed miscarriage usually does not cause any noticeable symptoms. Some women only discover it during a routine ultrasound, while others may experience changes like a loss of pregnancy symptoms, mild cramping, or dizziness.

READ: 10 Tips to Prepare for a Healthy Pregnancy After Miscarriage

8. Postpartum Lochia

After childbirth, your body sheds the uterine lining and blood that supported your baby during pregnancy. This process is called lochia and is a normal part of postpartum recovery.

Lochia typically lasts six to eight weeks, though this can vary from person to person. In the first few days, the discharge is often heavy and oxidised, giving it a dark or even black appearance.

As the oxidised blood is gradually expelled, the lochia changes in colour — transitioning from dark red or brownish-black to pinkish or brown, and eventually to yellow or creamy white. The flow also becomes lighter before stopping completely. Over this period, usually around 45 days, your uterus expels the remaining blood and tissue.

Remember that everyone heals at their own pace. Some women may experience lochia for a little longer, and that’s perfectly normal.

9. Cervical Cancer Risk

If you experience black blood with irregular bleeding, particularly after sexual activity or during menstruation, it could be an early indication of cervical cancer. Cervical cancer might not show any symptoms in the initial stages, but as the disease progresses, symptoms may include:

• Bloody or foul-smelling discharge
• Bleeding after sex
• Fatigue
• Weight loss
• Pain during sex
• Trouble urinating or defecating
• Pelvic pain
• Swollen legs

READ: What are the Causes of Common Period Problems?

10. Hormonal Changes, Stress, or Menopause

Sometimes, prolonged stress and depression can be one of the causes of black blood during menstruation. These emotional changes can alter the uterus's structure, thinning its walls and slowing its lining renewal. This delays cell shedding, leading to faster blood oxidation and dark brown or black periods.

Additionally, switching contraceptive pills may delay your period, allowing more time for the blood to oxidise, which can cause it to appear darker in colour.

The Bottom Line

If the only symptom you experience with black blood during your period is the colour, your uterus is likely shedding old, oxidised blood. This is a normal part of the menstrual cycle and doesn’t typically require medical treatment. However, if your flow is heavy and accompanied by other symptoms such as foul odour, pelvic or abdominal pain, fever, or difficulty urinating, it’s important to consult a doctor. They can help diagnose any underlying conditions and address potential issues.

Frequently Asked Questions (FAQs)