Does black blood mean infection? What to know about its causes

September 21, 2025 •

4 min read

Approximately 75% of women will experience at least one vaginal yeast infection in their lifetime, but many vaginal changes are unrelated to infection. While black blood might seem alarming, it is often a harmless result of oxidized blood and not an infection. Knowing the difference between normal and concerning symptoms is key to understanding your reproductive health.

Quick Summary

Black blood often signifies older, oxidized blood that has taken longer to exit the body, a natural and common occurrence during a menstrual cycle. However, black or dark discharge accompanied by other symptoms, such as a foul odor, pelvic pain, or fever, may point toward an underlying infection like PID or STIs and warrants medical evaluation.

Key Points

Normal Oxidation: Black blood is often just older blood that has oxidized, which is a normal process that happens when blood takes longer to leave the body, typically at the beginning or end of a menstrual cycle.
Look for Other Symptoms: Infection-related black blood is almost always accompanied by other signs like a foul odor, persistent pelvic pain, fever, or itching.
Foreign Objects Can Cause Infections: A forgotten tampon or other foreign object can obstruct blood flow and cause a blockage, leading to irritation and infection that may manifest as black discharge.
Infections Cause Inflammation: Pelvic Inflammatory Disease (PID) and STIs like chlamydia and gonorrhea can cause inflammation and irregular, sometimes dark, discharge.
Serious Conditions Are Possible: In rare cases, persistent and accompanied by other symptoms, black blood can be a sign of a more serious condition like a missed miscarriage or cervical cancer.
Consult a Doctor for Doubts: While a standalone instance of black blood is often benign, any associated unusual or concerning symptoms warrant a visit to a healthcare provider for a proper diagnosis and treatment.

Is Black Blood Always a Sign of Infection?

Experiencing black blood can be a startling experience, but it's important to understand that it is not always a sign of infection. In most cases, very dark brown or black discharge is simply older blood that has taken longer to exit the uterus. When blood is exposed to oxygen, a natural process of oxidation occurs, causing the color to darken. This is most common at the beginning or end of a menstrual cycle, when blood flow is lighter and slower.

While this can be alarming, especially for those who are used to a brighter red flow, it is a normal and harmless variation of a healthy menstrual cycle. The key to discerning a natural occurrence from a potential infection lies in the presence of other symptoms. An infection rarely causes black discharge in isolation and is almost always accompanied by other, more tell-tale signs.

Common and Harmless Causes of Black Blood

Start or End of a Period: During the first or last days of a period, the flow is often slower. The blood has more time to oxidize as it leaves the uterus, resulting in a darker, sometimes black, appearance. This is a very common and normal phenomenon.
Spotting: Light spotting, particularly between periods, can also be brown or black. This is typically older blood from the last menstrual cycle being cleared out by the body and is not usually a cause for concern.
Hormonal Fluctuations: Changes in hormone levels, such as those caused by birth control pills, perimenopause, or stress, can affect the timing and flow of your period. This can lead to irregular shedding of the uterine lining, causing blood to remain in the uterus longer and appear darker.
Postpartum Bleeding (Lochia): After childbirth, the body sheds blood and tissue from the uterus in a process called lochia. This discharge can start as a heavy, red flow and gradually become darker brown or black as it tapers off over several weeks.

When Black Blood May Indicate an Infection

While black blood alone is not typically an infection symptom, its appearance with other signs can be a warning. In these cases, the dark blood is often a result of inflammation or a blockage caused by bacteria. If you experience black discharge in combination with any of the following symptoms, it is important to seek medical advice:

Foul Odor: A strong, unpleasant, or "fishy" odor is a classic sign of a vaginal infection, such as bacterial vaginosis (BV) or a sexually transmitted infection (STI) like trichomoniasis.
Pelvic Pain and Cramping: While mild cramping is normal during a period, persistent or severe pelvic or abdominal pain, especially outside of your regular cycle, could indicate a more serious condition like Pelvic Inflammatory Disease (PID).
Fever and Chills: A fever and chills are systemic signs of an infection. When combined with black discharge, they are a clear signal to contact a healthcare provider.
Itching or Burning: Vaginal itching, burning, or irritation can be a symptom of a yeast infection, BV, or an STI. These symptoms often point toward inflammation caused by an infection.
Painful Urination or Sex: Pain during urination (dysuria) or painful intercourse (dyspareunia) can be associated with various infections affecting the reproductive tract.
Unexplained Bleeding: If you experience black discharge or spotting outside of your normal period, or after menopause, it could be a sign of an underlying issue that needs investigation.

The Role of Blockages and Forgotten Objects

In some cases, black blood can be caused by a physical blockage rather than an infection. One of the most common causes is a forgotten object in the vagina, such as a tampon or condom. This can obstruct the natural flow of blood and other fluids, causing them to pool and darken over time. The irritation can also lead to an infection. A blockage can also be caused by retained menses (hematocolpos), a rare condition where menstrual blood is trapped due to a structural abnormality in the reproductive tract. These situations are serious and require prompt medical attention.

Comparative Table: Normal vs. Concerning Black Blood


Characteristic	Normal Black Blood	Concerning Black Blood (Potential Infection)
Timing	Typically at the beginning or end of a period, or as light spotting.	Can occur at any time during the cycle, unexpectedly.
Associated Odor	Slight metallic or musty smell, typical of blood.	Strong, foul, or "fishy" odor.
Consistency	Thick, sticky, or resembling coffee grounds.	Can be accompanied by unusually heavy, clumpy, or watery discharge.
Accompanying Symptoms	None, or normal menstrual cramping.	Pelvic pain, fever, chills, vaginal itching, or burning.
Duration	Lasts for a day or two at the start/end of a cycle.	Persistent for several days or longer than usual.

Final Takeaway: What to Do Next

The most important step when you notice black blood is to consider the context. Is it the end of your period, with no other unusual symptoms? It's likely just old, oxidized blood. However, if it appears alongside a foul odor, fever, severe pain, or unexplained bleeding, these are red flags that point toward a potential infection or other medical issue. Ignoring these symptoms can lead to complications, such as PID, which can affect fertility. Therefore, if you have any doubts, it is always best to consult a healthcare professional for proper diagnosis and treatment. For more information on reproductive health, the Centers for Disease Control and Prevention provides excellent resources on sexually transmitted infections and general well-being.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Please consult a healthcare professional for any health concerns or before making any decisions related to your treatment.

Frequently Asked Questions

Black blood is considered normal at the very beginning or end of your period. This is because the flow is lighter and slower, giving the blood more time to oxidize and turn a dark brown or black color as it exits the body.

If your black blood is accompanied by a foul or fishy odor, severe pelvic pain, fever, itching, or pain during urination or sex, it may be a sign of an infection and should be checked by a doctor.

Yes, hormonal contraceptives can alter hormone levels, which may cause changes in your period flow and result in lighter or darker bleeding, including black spotting between periods, as your body adjusts.

Yes, a retained object such as a forgotten tampon or condom can cause a blockage. This can lead to irritation and infection, which may produce a black, foul-smelling discharge and warrants immediate medical attention.

PID is an infection of the female reproductive organs, often caused by untreated STIs. It can cause black discharge, pelvic pain, and fever. It requires prompt medical treatment to prevent serious complications like infertility.

In some cases, black bleeding or spotting can be a symptom of a missed miscarriage, where the embryo has stopped developing but remains in the uterus. If you are pregnant and experience black discharge, it's important to see a doctor.

You should see a doctor if black discharge occurs with a foul odor, fever, severe pain, or persists beyond your normal period. Also seek medical advice if you are pregnant, post-menopausal, or suspect a foreign object is lodged in your vagina.