Abnormal genital discharge most often points to one of a few causes: chlamydia, gonorrhea, trichomoniasis, or bacterial vaginosis (BV). It can also come from a yeast infection or simply be normal physiological discharge. Because these conditions look so much alike, and several cause no symptoms, only a lab test can confirm which one, if any, you have.
Comparison
| Item | % of cases without symptoms |
|---|---|
| Chlamydia | ~70% |
| Gonorrhea | ~75% |
| Trichomoniasis | ~70% |
| Bacterial vaginosis | ~50% |
Which STIs cause abnormal genital discharge?
Four conditions account for the large majority of discharge complaints clinicians evaluate. Three are sexually transmitted infections; one (BV) isn't strictly an STI but is closely linked to sexual activity and shows up in the same workup. Below is how each one tends to behave, and why the pattern alone won't get you to a diagnosis.
Chlamydia
Chlamydia is caused by the bacterium Chlamydia trachomatis, and most US genital infections are the serovars D. K CDC. It usually causes nothing at all: roughly three quarters of infected women and half of infected men notice no symptoms. When women do have symptoms, the classic ones are abnormal vaginal discharge and burning on urination. If the infection climbs higher into the reproductive tract, it can add lower abdominal or low-back pain, fever, pain during intercourse, and bleeding between periods, signals that it may be progressing toward pelvic inflammatory disease (infection of the uterus and tubes, which can scar them and threaten fertility). When symptoms do appear, they usually show up within one to three weeks after exposure. Learn more about chlamydia and how it's caught.
Gonorrhea
Gonorrhea comes from the bacterium Neisseria gonorrhoeae, which can infect the genitals, rectum, and throat CDC. In men it tends to announce itself: burning when urinating and a white, yellow, or green penile discharge are the hallmark, and less commonly swollen or painful testicles (epididymitis, inflammation of the tube behind the testicle that can affect fertility). In women it's often quiet, with most having no symptoms; when present, they include painful or burning urination, increased vaginal discharge, and bleeding between periods. The thicker, more obviously colored discharge in men is a useful clue, but it overlaps enough with other infections that it can't stand in for testing. See the full picture of gonorrhea.
Trichomoniasis
Trichomoniasis is caused by the protozoan parasite Trichomonas vaginalis and is the most common curable STI CDC. About 70% of infected people have no signs at all. In women the textbook presentation is itching, burning, redness or soreness of the genitals, discomfort urinating, and a clear, white, yellowish, or greenish discharge with a fishy smell. Men, who are commonly asymptomatic, may notice itching or irritation inside the penis, burning after urinating or ejaculating, and discharge. Symptoms, when they appear, may show up about 5 to 28 days after infection, but they can also surface much later, so timing rarely pins down trichomoniasis on its own. Review the full list of trichomoniasis symptoms.
Bacterial vaginosis (BV)
BV isn't an infection passed from a partner so much as an imbalance: the normal Lactobacillus species that keep the vagina slightly acidic get crowded out by anaerobic bacteria. It's the most common vaginal condition in women ages 15–44 CDC. The signature is a thin white or gray discharge with a strong fish-like odor, classically more noticeable after sex, sometimes with itching, burning, or burning when urinating. Like the others, BV is frequently silent. Because it can recur, it helps to understand how to prevent BV.
When it's NOT an STI
Not every change in discharge means an infection you caught from someone. A yeast infection (overgrowth of Candida, a normal vaginal fungus) is a common culprit, typically bringing a thick, white, cottage-cheese-like discharge with intense itching rather than odor. And plenty of discharge is simply normal physiological discharge that shifts in amount and texture across the menstrual cycle, with arousal, or with hormonal changes. The trouble is that yeast, BV, and trichomoniasis can all itch, and several conditions can produce a whitish discharge, so 'it looks like yeast' is a guess rather than a diagnosis.
How to tell them apart
There are discriminating features clinicians lean on: odor, color, consistency, itch, and timing. But they're tendencies, not rules. A fishy odor that's worse after sex nudges toward BV or trichomoniasis; a thick, odorless, intensely itchy discharge nudges toward yeast; a colored penile discharge with burning nudges toward gonorrhea. Even so, these patterns overlap too much to settle by sight alone, and several are frequently silent. A test is what tells you which one, if any, it is.
This overlap is why self-diagnosis fails so often here. People treat themselves for yeast when they actually have BV or trichomoniasis, lose time, and risk passing an infection along. A test turns the guess into an answer.
Discharge causes at a glance
| Cause | Typical discharge | Odor | Other clues | Often silent? |
|---|---|---|---|---|
| Chlamydia | Abnormal vaginal discharge (women); variable | Not characteristic | Burning urination; bleeding between periods if it spreads | Yes: ~3/4 of women, ~1/2 of men |
| Gonorrhea | White, yellow, or green (penile discharge in men) | Not characteristic | Painful urination; women often symptom-free | Yes: most women |
| Trichomoniasis | Clear, white, yellowish, or greenish | Fishy | Itching, soreness, burning urination | Yes: about 70% of people |
| Bacterial vaginosis | Thin white or gray | Strong fishy, worse after sex | Itching/burning; vaginal pH >4.5 | Yes: many have no symptoms |
| Yeast (not an STI) | Thick, white, clumpy | Little or none | Intense itching | Usually symptomatic |
How it's tested
For the three STIs, a nucleic acid amplification test (NAAT) is the preferred method, detecting the organism's genetic material from a urine sample or a swab. NAAT is the recommended test for chlamydia CDC, 2021, the preferred screening test for gonorrhea (sensitivity usually above 90%, specificity around 99%), and the preferred test for trichomoniasis (with assays reaching roughly 95–100% sensitivity). 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 (the reference standard), or an FDA-cleared molecular test. In practice testing means a urine sample, a self-collected swab, or a quick exam depending on what's suspected; it's free or low-cost at health departments, Planned Parenthood, and Title X clinics, with results usually back in a few days. Here's where to get tested.
What to do next
All four conditions are treatable, and the STIs among them are curable. Get a test, then the specific treatment matched to your result. Don't start over-the-counter yeast products on a hunch, since that delays care if it's actually BV, trichomoniasis, or an STI. If you had a recent exposure, timing matters for accuracy; check when to test after exposure so you don't test too early and get a falsely reassuring result.
Red flags, when to get seen urgently
- Lower abdominal or pelvic pain, especially with fever, a possible sign that infection has spread to the uterus and tubes.
- Pain during intercourse or bleeding between periods alongside discharge.
- Swollen or painful testicles in men, which can signal epididymitis.
- Discharge with a high fever or feeling generally unwell.
- Symptoms during pregnancy, since some of these infections can affect the pregnancy and the newborn.
- Symptoms that worsen or don't improve after starting treatment.
Keep exploring on EasySTD: which STD test you need, what STD testing costs and Bacterial vaginosis testing.