Green vaginal discharge almost always signals an infection. The green color comes from your immune system fighting back: white blood cells called neutrophils rush to the site of infection, and they contain a green-colored enzyme that makes up about 5% of their dry weight. The more neutrophils your body sends, the greener the discharge appears. While the color itself isn’t dangerous, the underlying infection needs treatment.
Why Discharge Turns Green
Normal vaginal discharge ranges from clear to milky white. When bacteria or parasites invade, your body floods the area with neutrophils to kill the invaders. These immune cells are packed with an enzyme that happens to be naturally green. As neutrophils accumulate and break down at the infection site, they tint the discharge yellow-green or fully green. A foul or fishy smell alongside the color change further confirms that something infectious is going on, not just a normal fluctuation in your cycle.
Trichomoniasis
Trichomoniasis is the most common curable STI and one of the top reasons for green discharge. It’s caused by a tiny parasite, and the hallmark is thin or frothy discharge that can be clear, white, yellow, or green, usually with a strong fishy odor. You might also notice itching, burning during urination, or irritation around the vulva.
Many people with trichomoniasis have mild symptoms or none at all, which means it can go undiagnosed for weeks or months. If you’re sexually active and notice green, frothy discharge with an odor, this infection is high on the list of possibilities. Treatment is a course of oral antibiotics taken twice daily for seven days. Sexual partners need to be treated at the same time, even if they have no symptoms, because reinfection is common otherwise. Most men with trichomoniasis never develop symptoms but can still pass the parasite back to you.
Gonorrhea and Chlamydia
Gonorrhea, the second most common STI in the United States, can produce yellow to yellow-green discharge that looks different from your normal. Other signs include bleeding between periods, pain during urination, and rectal discomfort if the infection has spread there. Symptoms tend to show up within a few days to two weeks of exposure.
Chlamydia, the most common STI overall, is trickier because it usually causes no symptoms at all. When it does, the signs overlap heavily with gonorrhea: abnormal yellow discharge, bleeding between periods, and painful urination. These symptoms are often mild enough to be mistaken for a urinary tract infection or a yeast infection. Because the two infections look so similar and frequently occur together, testing for both at the same time is standard practice.
Bacterial Vaginosis
Bacterial vaginosis (BV) isn’t an STI, but it can produce discharge that ranges from grayish-white to yellowish-green. It happens when the balance of bacteria in the vagina shifts, allowing certain types to overgrow. The signature clue is a strong fishy smell, especially after sex. BV discharge tends to be thinner and more uniform than the frothy texture seen with trichomoniasis, but the overlap in symptoms makes it hard to tell the two apart without testing.
BV is extremely common and can resolve on its own in some cases, but it often recurs. It raises the vaginal pH above its normal acidic range (above 4.5), which also makes you more vulnerable to picking up other infections, including STIs.
How the Cause Is Identified
A healthcare provider can often narrow things down with a few simple steps during an office visit. They’ll check the pH of your vaginal fluid using a small strip of pH paper. A reading above 4.5 points toward BV or trichomoniasis, though it doesn’t distinguish between the two. Next, a sample of the discharge is placed on a slide and examined under a microscope. In trichomoniasis, the parasites are sometimes visible swimming around on the slide. In BV, the cells have a distinctive fuzzy appearance caused by bacteria coating their edges.
Microscopy catches only about half of trichomoniasis cases, though, so a more sensitive molecular test (called a NAAT) is used when the microscope doesn’t show anything definitive. Gonorrhea and chlamydia are diagnosed through the same type of molecular test, usually from a vaginal swab or urine sample. Results typically come back within a few days.
What Happens if You Wait Too Long
Ignoring green discharge and hoping it resolves is risky. Untreated gonorrhea and chlamydia can spread from the vagina up into the uterus and fallopian tubes, causing pelvic inflammatory disease (PID). PID creates scar tissue and pockets of infected fluid in the reproductive tract, and the damage can be permanent. Each episode of PID increases your risk of infertility, and delaying treatment makes that risk significantly worse.
Even BV and trichomoniasis, which might seem less serious, carry consequences if left alone. Both raise your susceptibility to other sexually transmitted infections, including HIV. And if you become pregnant while infected, the risks extend to the baby.
Green Discharge During Pregnancy
Infections that cause green discharge are especially concerning during pregnancy. Trichomoniasis is linked to premature rupture of membranes, preterm delivery, and low birth weight. Bacterial vaginosis carries similar risks: preterm labor, early membrane rupture, and postpartum uterine infection. One study in the Pakistan Journal of Medical Sciences found that pathological vaginal discharge during pregnancy was significantly associated with both preterm delivery and low birth weight.
If you’re pregnant and notice a change in your discharge color or smell, getting tested promptly matters. The infections themselves are treatable during pregnancy, and early treatment reduces the chance of complications for both you and the baby.
Green vs. Yellow Discharge
The line between yellow and green discharge isn’t always clear-cut, and both can signal the same infections. What matters more than the exact shade is the combination of signs: color that’s different from your normal, an unusual smell, itching, burning, or pain. Bright or dark green discharge with a foul odor is more concerning than a slightly yellowish tint with no other symptoms. But even pale yellow-green discharge deserves attention if it comes with any of those additional warning signs or if it persists for more than a day or two.