Abnormal genital discharge is most often caused by a handful of treatable infections: chlamydia, gonorrhea, and trichomoniasis among the STIs, plus bacterial vaginosis (BV) and yeast infections, which aren't classic STIs. These conditions overlap too much to tell apart by looks or smell alone. Only a test confirms which one (if any) you have.
often silent; discharge or burning if anything
discharge and burning; can also hit throat/rectum
frothy, itchy discharge with an odor
thin grey discharge, fishy odor (not an STI)
| Item | Value |
|---|---|
| Chlamydia | curable — often silent; discharge or burning if anything |
| Gonorrhea | curable — discharge and burning; can also hit throat/rectum |
| Trichomoniasis | curable — frothy, itchy discharge with an odor |
| Bacterial vaginosis (BV) | curable — thin grey discharge, fishy odor (not an STI) |
The short list of likely causes
When discharge changes color, volume, smell, or texture, the usual suspects fall into two buckets. The STI causes are chlamydia, gonorrhea, and trichomoniasis. The non-STI causes are bacterial vaginosis (a shift in the vaginal bacteria, not something caught from a partner in the usual sense) and yeast infections. Normal physiological discharge also shifts across the menstrual cycle, so not every change means infection at all.
Several of these are frequently silent, and the ones that do cause discharge produce patterns that blur into each other. Only a test settles it.
Which STIs cause abnormal genital discharge
Chlamydia
Chlamydia is caused by the bacterium Chlamydia trachomatis, and most US genital infections come from serovars D–K CDC. Roughly three quarters of infected women and half of infected men notice nothing at all. When women do have symptoms, they include abnormal vaginal discharge and burning on urination. If the infection climbs into the upper reproductive tract, it can add lower abdominal or low-back pain, fever, pain during sex, and bleeding between periods — signs the bacteria may be causing pelvic inflammatory disease (inflammation of the uterus, tubes, and ovaries that can scar the tubes and threaten fertility).
If symptoms appear at all, they usually show up within one to three weeks after exposure. Because so many cases are symptom-free, feeling fine tells you nothing. Reinfection is common after treatment, so follow-up testing matters; here's how chlamydia reinfection is caught.
Gonorrhea
Gonorrhea is caused by the bacterium Neisseria gonorrhoeae, which can infect the genitals, rectum, and throat CDC, About Gonorrhea. In men it tends to announce itself: burning when urinating and a white, yellow, or green penile discharge, and less commonly swollen or painful testicles (a sign of epididymitis — inflammation of the coiled tube behind the testicle that can affect fertility). In women, most have no symptoms; when they do, it's painful or burning urination, increased vaginal discharge, and bleeding between periods.
The thick, colored penile discharge of gonorrhea is one of the more distinctive presentations, but color alone can't separate it from other causes reliably — both gonorrhea and trichomoniasis can produce a yellow-green discharge. A lab test sorts it out; see how a gonorrhea test works and what the results mean.
Trichomoniasis
Trichomoniasis is caused by the protozoan parasite Trichomonas vaginalis and is the most common curable STI CDC, About Trich. About 70% of infected people have no signs or symptoms. When women have symptoms, it's itching, burning, redness or soreness of the genitals, discomfort urinating, and a clear, white, yellowish, or greenish discharge that often carries a fishy smell. Men usually feel nothing, though some get itching or irritation inside the penis, burning after urinating or ejaculating, and discharge.
Symptoms, when they appear, may show up roughly 5 to 28 days after infection, but they can also surface much later, so a recent exposure isn't required to explain new symptoms. Read more on trichomoniasis testing & diagnosis if this fits your picture.
Bacterial vaginosis (BV)
BV isn't a classic STI, but it's the most common cause of abnormal discharge in women ages 15–44 CDC, About BV. It comes from an imbalance: the protective Lactobacillus bacteria that normally dominate the vagina get crowded out by anaerobic bacteria. The hallmark is a thin white or gray discharge with a strong fish-like odor, often most noticeable after sex, sometimes with itching, burning, or burning on urination. As with the others, many people with BV have no symptoms at all. More on the full picture of bv symptoms.
When it's not an STI
Abnormal discharge isn't always an infection you caught from a partner. A yeast infection (an overgrowth of Candida) classically causes a thick, white, clumpy discharge with intense itching and usually no odor, a different profile from BV's thin, fishy discharge. And normal physiological discharge changes in amount and consistency across the menstrual cycle, around ovulation, and with hormonal birth control. BV is technically a microbiome imbalance rather than a transmitted pathogen, though sexual activity influences it.
How to tell them apart
Clinicians look at the pattern — color, consistency, odor, itch, and urinary symptoms together — rather than any single feature, because no one sign is specific enough to stand alone. A fishy odor that worsens after sex points toward BV or trichomoniasis. Intense itch with thick white discharge and no smell leans toward yeast. Thick colored penile discharge with painful urination suggests gonorrhea. These are tendencies, not proof.
Overlapping symptoms are why you usually can't self-diagnose this. Several of these infections are frequently silent, and the ones that aren't produce look-alike discharge. A test turns a guess into an answer. Treat the wrong cause — buy a yeast cream when it's really trichomoniasis — and you waste time while an untreated infection keeps doing damage.
Side-by-side comparison
| Cause | Typical discharge | Odor | Other clues | Often silent? |
|---|---|---|---|---|
| Chlamydia | Abnormal vaginal discharge; mucus-like | Not characteristic | Burning on urination; bleeding between periods | Yes — most cases |
| Gonorrhea | Increased vaginal discharge; white/yellow/green penile discharge | Not characteristic | Painful urination; testicular pain in men | Often in women |
| Trichomoniasis | Clear, white, yellow, or green | Often fishy | Itching, soreness, urinary discomfort | Yes — about 70% |
| Bacterial vaginosis | Thin, white or gray | Strong fishy, worse after sex | Itching/burning; burning on urination | Often |
| Yeast infection | Thick, white, clumpy | Usually none | Intense itch | No — usually symptomatic |
How it's tested
For chlamydia, gonorrhea, and trichomoniasis, a nucleic acid amplification test (NAAT) is the preferred method — it's the most sensitive way to detect the organism's DNA or RNA from a urine sample or a swab CDC STI Treatment Guidelines, 2021. Gonorrhea NAAT runs at high sensitivity (usually above 90%) with specificity around 99%, and the trichomoniasis NAAT (such as the Aptima assay) reaches roughly 95–100% sensitivity on vaginal swabs and female urine CDC, Trich Tx. BV is diagnosed differently — by the Amsel criteria (thin discharge, clue cells, vaginal pH above 4.5, and a positive whiff test), a Nugent score on Gram stain, or an FDA-cleared molecular test CDC, BV Tx. The full how-to is on our page about how to get tested.
Depending on what's suspected, testing is a urine sample, a self-collected swab, or a quick exam. It's free or low-cost at health departments, Planned Parenthood, and Title X clinics, and results are usually back in a few days. If you're timing a test around a recent exposure, check when to test after exposure so you don't test too early and read a false negative as reassurance.
What to do next
Don't treat blindly. Get the right test, get the result, and match treatment to the actual cause. Chlamydia, gonorrhea, and trichomoniasis are all curable with antibiotics or antiparasitic medication, and BV is treated with its own antibiotics. Partners often need treatment too, and retesting is recommended for several of these because reinfection is common. Specific regimens and follow-up live on the treatment page.
Red flags — when to get seen urgently
- Fever with lower abdominal or pelvic pain, which can signal pelvic inflammatory disease and needs prompt care.
- Severe pain, swelling, or a painful testicle, which may mean the infection has spread.
- Discharge during pregnancy, since several of these infections affect pregnancy outcomes and need treatment.
- Discharge with sores, ulcers, or significant genital pain, which points toward causes beyond the ones covered here.
- Symptoms that don't improve after treatment, which may mean the wrong cause was treated or reinfection occurred.