Green 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 an enzyme with a naturally green pigment. The more neutrophils concentrated in the discharge, the greener it looks. So green discharge is essentially visible evidence that your body is battling something, and the most common culprits are sexually transmitted infections.
Why Discharge Turns Green
Neutrophils, the most common type of white blood cell, are packed with an enzyme that was originally named “verdeperoxidase” because of its vivid green color. This enzyme contains an iron-based pigment similar to what makes blood red, except its chemical structure reflects green light instead. When a large number of neutrophils flood into vaginal fluid, cervical mucus, or urethral secretions, the discharge takes on a yellow-green to green appearance. The same process gives pus its color in infected wounds.
This means green discharge isn’t caused by the bacteria or parasites themselves. It’s caused by your immune response to them. The greener and thicker the discharge, the more intense the immune reaction.
Trichomoniasis: The Most Common Cause
Trichomoniasis is the most prevalent nonviral sexually transmitted infection worldwide, affecting roughly 2.6 million people in the United States alone. It’s caused by a single-celled parasite and is the infection most closely associated with green discharge. The classic presentation is a profuse, frothy, yellow-green discharge with a strong, unpleasant odor that’s often described as fishy.
Other symptoms that typically accompany trichomoniasis include vaginal itching, burning, or soreness, pain during sex, and a burning sensation when urinating. That said, many people with trichomoniasis have no symptoms at all. Symptomatic women are about four times more likely to test positive than asymptomatic women (26% versus 6.5%), which means a significant number of infections go unnoticed and untreated.
In men, trichomoniasis can cause urethral irritation and discharge, though it often produces no symptoms. Prevalence varies significantly by region and population, with rates ranging from under 1% to nearly 10% in some groups.
Gonorrhea and Chlamydia
Gonorrhea produces a thick, cloudy, or sometimes bloody discharge from the vagina or penis. It can appear yellowish or greenish, particularly in men, where purulent (pus-filled) urethral discharge is a hallmark symptom. Accompanying symptoms include painful urination, bleeding between periods, and pelvic pain.
Chlamydia can also cause abnormal discharge, though it tends to be less dramatic in appearance than gonorrhea. The two infections frequently occur together. Chlamydia is responsible for 15% to 40% of non-gonococcal urethritis cases in men, and both infections can be present without obvious symptoms, especially in women.
A newer concern is Mycoplasma genitalium, which accounts for 15% to 25% of non-gonococcal urethritis cases in the U.S. and can produce similar discharge symptoms.
How Green Discharge Differs From Other Types
Not all abnormal discharge is green, and the color and consistency offer useful clues about what’s going on:
- Green or yellow-green, frothy, foul-smelling: Most characteristic of trichomoniasis.
- Thick, cloudy, or yellowish: More typical of gonorrhea.
- Thin, off-white or grayish, fishy odor: Characteristic of bacterial vaginosis (BV). BV is not an STI but an imbalance in vaginal bacteria. It rarely causes green discharge on its own.
- Thick, white, cottage cheese-like: Typical of a yeast infection.
If your discharge is clearly green rather than white or gray, an STI is more likely than BV or a yeast infection. The presence of a strong odor and irritation makes this even more probable.
Green Discharge in Men
Men searching this term are likely noticing discharge from the urethra. Any visible discharge from the penis, whether mucoid, cloudy, or green, is considered a sign of urethritis (inflammation of the urethra). Gonorrhea is the most common cause of purulent, greenish urethral discharge. When gram-stain microscopy doesn’t show gonorrhea, the diagnosis shifts to non-gonococcal urethritis, which can be caused by chlamydia, Mycoplasma genitalium, trichomoniasis, or, less commonly, viral infections like herpes simplex virus or adenovirus.
How It’s Diagnosed
A simple visual exam isn’t enough to identify the exact cause of green discharge. The traditional method, a wet mount microscopy where a sample is examined under a microscope, catches trichomoniasis only about 50% to 70% of the time. It’s highly specific (if the parasite is seen, it’s definitely there), but it misses a lot of cases.
Modern molecular tests, called nucleic acid amplification tests, are far more accurate. These detect the genetic material of the organism and achieve sensitivity rates of 95% to 100% for trichomoniasis, depending on the sample type. Vaginal swabs tend to be the most reliable. These same testing platforms can simultaneously check for gonorrhea and chlamydia, making it possible to screen for multiple infections from a single sample.
Rapid point-of-care tests are also available and detect trichomoniasis with about 83% to 92% sensitivity, which is a significant improvement over wet mount microscopy.
Risks During Pregnancy
Green discharge during pregnancy deserves prompt attention. Vaginal infections during pregnancy can trigger the release of inflammatory compounds that stimulate uterine contractions, raising the risk of preterm labor. Infection can also lead to premature rupture of the membranes, where the fluid-filled sac around the baby breaks too early. Bacteria can produce enzymes that directly damage the membranes.
Bacterial vaginosis during pregnancy is associated with preterm labor, spontaneous abortion, placental infection, and postpartum complications like uterine infection. Trichomoniasis carries similar risks. These aren’t rare complications: infection-related inflammation is one of the leading contributors to premature birth, which significantly increases health risks for the newborn.
Warning Signs of a Spreading Infection
Green discharge on its own points to a localized infection. But certain additional symptoms suggest the infection has spread beyond the vagina or urethra into the reproductive organs, a condition called pelvic inflammatory disease (PID) in women:
- Lower abdominal or pelvic pain
- Fever
- Pain or bleeding during sex
- Burning with urination
- Bleeding between periods
PID can damage the fallopian tubes, leading to chronic pelvic pain, ectopic pregnancy, or infertility. It develops when STIs like gonorrhea or chlamydia move upward from the cervix. The presence of any of these symptoms alongside green discharge makes testing and treatment more urgent.
Treatment and What to Expect
All of the infections that cause green discharge are treatable with antibiotics or antiparasitic medications. Trichomoniasis is treated with a course of oral antiparasitic medication. Gonorrhea and chlamydia each have their own antibiotic regimens. Because these infections frequently overlap, it’s common to be treated for more than one at the same time.
Sexual partners need treatment too, even if they have no symptoms. Reinfection is common when partners aren’t treated simultaneously. You should avoid sexual contact until both you and your partner have completed treatment. For trichomoniasis specifically, a follow-up test is recommended a few weeks after treatment to confirm the infection has cleared, since reinfection rates are high.