Green vaginal or penile discharge is most commonly caused by trichomoniasis, a sexually transmitted infection caused by a microscopic parasite. Gonorrhea can also produce discharge with a greenish or yellowish tint, though it more often appears white or pus-like. Both infections are curable with antibiotics, but they require different treatments, so getting tested matters more than guessing based on color alone.
Trichomoniasis: The Most Common Cause
Trichomoniasis is the STI most strongly associated with green discharge. The CDC describes the typical discharge as “clear, white, yellowish, or greenish” with a fishy smell. It can also appear thin or frothy, and the volume often increases noticeably. About 3.7 million people in the U.S. have trichomoniasis at any given time, making it one of the most common curable STIs.
The infection is caused by a single-celled parasite called Trichomonas vaginalis. In women, it infects the vagina, vulva, and urethra. In men, it typically infects the urethra. Only about 30% of people with trichomoniasis develop symptoms, which means many carry and spread it without knowing. When symptoms do appear, they usually show up within 5 to 28 days of exposure, though some people develop symptoms much later.
Beyond discharge, trichomoniasis can cause itching, burning, redness, or soreness around the genitals. Urination may sting, and sex can become uncomfortable. Men often experience irritation inside the penis or a mild discharge after urination.
Gonorrhea and Discharge Color
Gonorrhea is the other STI that can produce greenish or yellow-green discharge, though it’s more commonly described as “pus-like.” In men, this discharge typically appears at the tip of the penis and is often thick and noticeable. Women may see increased vaginal discharge, but it tends to be less distinctly colored and easier to overlook.
Gonorrhea can also infect the rectum and eyes. Rectal gonorrhea produces pus-like discharge from the anus along with soreness and itching. Eye infections cause discharge from one or both eyes and can threaten vision if untreated. Many women with gonorrhea have no symptoms at all, or they mistake symptoms for a bladder or vaginal infection.
The key difference from trichomoniasis: gonorrhea discharge tends to be thicker and more opaque, while trichomoniasis discharge is often thinner, frothier, and more likely to have that distinctive fishy odor. But these distinctions aren’t reliable enough to self-diagnose. Both infections need lab confirmation.
What About Bacterial Vaginosis?
Bacterial vaginosis (BV) is sometimes confused with trichomoniasis because both can cause a fishy-smelling discharge. However, BV discharge is typically thin, white, or gray, not green. BV is also not an STI. It results from an imbalance of natural vaginal bacteria and doesn’t involve a parasite or require partner treatment. If your discharge is clearly green or yellow-green, trichomoniasis or gonorrhea is more likely than BV.
How These Infections Are Diagnosed
Your provider will usually start with a “wet prep,” which involves looking at a sample of your discharge under a microscope. This test is fast and cheap, but it misses infections fairly often. If the wet prep comes back negative but your symptoms point to trichomoniasis, more sensitive follow-up tests are available.
Nucleic acid amplification tests (NAATs) detect genetic material from the parasite and are considerably more accurate. Rapid antigen tests, done only on vaginal fluid, can return results in under 15 minutes. Culture tests take up to a week because the lab grows the sample to make parasites easier to spot. For gonorrhea, a NAAT on a urine sample or swab is the standard approach.
Testing for both infections at the same time is common practice, since their symptoms overlap and co-infection is possible.
Treatment for Each Infection
Trichomoniasis and gonorrhea are both curable, but they require completely different medications.
For trichomoniasis, the CDC recommends a week-long course of oral antibiotics for women, taken twice daily. Men are typically given a single, larger dose of the same medication. An alternative single-dose option exists for both. Women living with HIV follow the same seven-day regimen. You should avoid alcohol during treatment and for at least 24 hours afterward, because the medication interacts with it and can cause nausea and vomiting.
Gonorrhea requires a single injection of an antibiotic. This is the only CDC-recommended treatment for uncomplicated gonorrhea, and oral alternatives are not considered reliable due to rising antibiotic resistance. You’ll receive the injection at your provider’s office or a clinic.
Why Your Partner Needs Treatment Too
Both trichomoniasis and gonorrhea pass easily between sexual partners, and reinfection after treatment is extremely common if your partner isn’t treated at the same time. Many states allow something called expedited partner therapy (EPT), where your provider gives you a prescription or extra medication to bring directly to your partner, even if that partner hasn’t been examined. This removes the barrier of your partner needing to schedule their own appointment.
You should avoid sex until both you and your partner have completed treatment and any symptoms have resolved. For trichomoniasis, retesting about three months after treatment is recommended because reinfection rates are high.
Risks of Leaving It Untreated
Untreated trichomoniasis increases susceptibility to HIV. The inflammation it causes in genital tissue makes it easier for HIV to enter the body during sex. During pregnancy, trichomoniasis raises the risk of preterm delivery and low birth weight.
Untreated gonorrhea can spread to the blood, joints, or heart valves, a rare but serious complication. In women, it can travel into the uterus and fallopian tubes, causing pelvic inflammatory disease, chronic pain, and fertility problems. In men, it can cause painful inflammation in the tubes near the testicles.
Because both infections are so easily cured, the main risk isn’t the disease itself. It’s the delay in getting tested.