What causes black discharge during menstruation?

Black Discharge During Menstruation

Black discharge during menstruation is typically normal and represents older blood that has taken longer to exit the uterus, oxidizing and darkening in color before being expelled. This is a benign physiological variation in menstrual flow and does not require treatment in most cases.

Understanding Normal Menstrual Discharge Color Variation

• Menstrual blood color varies naturally from bright red (fresh blood) to dark brown or black (older, oxidized blood) depending on how long the blood remains in the uterus before being expelled 1
• Blood comprises only 36% of total menstrual fluid on average (range 1.6-81.7%), with the remainder being endometrial tissue fluid, which can affect the appearance and color of discharge 1
• Black discharge most commonly occurs at the beginning or end of menstruation when flow is lighter and blood moves more slowly through the reproductive tract, allowing more time for oxidation

When Black Discharge is Normal (Physiologic)

Black discharge is typically benign when it:

• Occurs at the start or end of your period 1
• Is not accompanied by foul odor 2
• Does not cause significant vulvar irritation or itching 2
• Is not associated with fever, severe pain, or other systemic symptoms

When to Investigate Further (Pathologic Causes)

You should seek medical evaluation if black discharge is accompanied by:

Warning Signs Requiring Assessment

• Foul-smelling odor suggesting bacterial vaginosis or other infection 2, 3
• Significant vulvar itching or irritation suggesting candidiasis or other vulvovaginal infection 2, 4
• Pelvic pain or fever suggesting pelvic inflammatory disease 2
• Discharge between periods or unrelated to menstruation 2
• Heavy bleeding with flooding (changing pad/tampon more than hourly) or clots ≥1 inch, suggesting heavy menstrual bleeding that may require evaluation for bleeding disorders or structural abnormalities 5

Diagnostic Approach When Pathology is Suspected

If abnormal characteristics are present, perform:

• Vaginal pH testing - normal pH is <4.5; elevated pH (>4.5) suggests bacterial vaginosis or trichomoniasis 2, 3
• Wet mount microscopy of vaginal secretions in saline to identify clue cells (bacterial vaginosis), motile trichomonads, or white blood cells indicating infection 2
• KOH preparation to identify yeast/pseudohyphae (candidiasis) and perform whiff test (fishy odor indicates bacterial vaginosis) 2, 3
• Pelvic examination to assess for cervical friability, lesions, or signs of pelvic inflammatory disease 2

Common Pitfalls to Avoid

• Do not assume all dark discharge is pathologic - oxidized blood is a normal variant and the most common cause of black menstrual discharge 1
• Do not overlook infection if foul odor is present - bacterial vaginosis is the most prevalent cause of vaginal discharge with malodor, affecting up to 50% of women asymptomatically 2, 3
• Do not dismiss heavy menstrual bleeding - if black discharge is accompanied by flooding or large clots, evaluate for bleeding disorders or structural abnormalities 5
• Recognize that vaginal discharge assessment requires objective testing - visual inspection alone is insufficient; pH and microscopy are essential for accurate diagnosis 2, 4

Treatment Considerations

For normal black discharge (oxidized blood):

• Reassurance that this is a normal physiological variant 1
• No treatment required

For pathologic discharge with infection:

• Bacterial vaginosis: metronidazole 500 mg orally twice daily for 7 days 3
• Candidiasis: antifungal therapy based on culture results 2, 4
• Trichomoniasis: appropriate antiprotozoal therapy 2, 4

The key distinction is whether the black discharge occurs during normal menstruation without other symptoms (reassurance only) versus discharge with abnormal characteristics requiring diagnostic workup and treatment.