Bacterial vaginosis, a yeast infection, and trichomoniasis are the three conditions most often confused with each other. BV usually brings a thin gray discharge with a fishy odor; a yeast infection brings thick white discharge with intense itching and no smell; trich often brings a frothy yellow-green discharge, sometimes fishy. Symptoms overlap heavily, so a test is what tells them apart.
most common curable STI; metronidazole
not an STI; recurs in up to 60%
not an STI; antifungal cure
| Item | Value |
|---|---|
| Trichomoniasis | curable — most common curable STI; metronidazole |
| Bacterial vaginosis (BV) | curable — not an STI; recurs in up to 60% |
| Vaginal yeast infection (candidiasis) | curable — not an STI; antifungal cure |
What each one is
Trichomoniasis
Trichomoniasis is caused by a single-celled parasite called Trichomonas vaginalis, the most common curable sexually transmitted infection CDC. It spreads through sexual contact. It's also the most common curable non-viral STI in the US, with an estimated 2.6 million infections, and it lands disproportionately on women, who account for over 80% of cases Sex Transm Dis, 2018. Because it's a true STI, a diagnosis means partners need treatment too.
Bacterial vaginosis (BV)
BV is an imbalance of the vaginal microbiome: the protective Lactobacillus species that normally keep the environment acidic get crowded out by anaerobic bacteria. It's the most common vaginal condition in women ages 15–44 CDC. BV isn't classed as an STI in the traditional sense, and you can develop it without any new partner, but sexual activity changes the vaginal flora and raises the odds. Read more on the full range of bv symptoms.
Vaginal yeast infection (candidiasis)
A yeast infection is a fungal overgrowth, usually of Candida albicans, which lives harmlessly in small amounts until antibiotics, pregnancy, diabetes, or a weakened immune system lets it bloom CDC. It's one of the most common fungal infections and is not usually acquired through sex, so it isn't an STI and partners generally don't need treatment. See the full picture of yeast infection symptoms.
Symptoms compared
All three can cause itching, burning, abnormal discharge, and discomfort urinating, and all three can cause no symptoms at all. About 70% of people with trichomoniasis have no signs whatsoever, and many people with BV are also symptom-free.
- Trichomoniasis (women): itching, burning, redness or soreness of the genitals; discomfort urinating; and a clear, white, yellowish, or greenish discharge with a fishy smell. In men it's usually silent, but can cause itching inside the penis, burning after urinating or ejaculating, and discharge.
- BV: a thin white or gray discharge; a strong fish-like odor that's especially noticeable after sex; sometimes itching, burning, or burning when urinating. The odor is the most distinctive clue.
- Yeast infection: vaginal itching or soreness (often intense), abnormal discharge that's typically thick and white, pain during sex, and discomfort urinating. Severe cases bring redness, swelling, and small cracks in the vaginal wall, with no fishy odor.
How to tell them apart
A few features point in different directions. Odor is one of the strongest: a fishy smell suggests BV or sometimes trich, while yeast infections typically don't smell. Texture matters too. Thick and cottage-cheese-like leans toward yeast, thin and gray leans toward BV, and frothy yellow-green leans toward trich. Vaginal pH separates them in the clinic, with BV and trich raising pH above normal while a yeast infection keeps pH in the normal range.
The symptoms overlap enough that you usually can't tell these apart by feel. The most common over-the-counter mistake is treating a presumed yeast infection that turns out to be BV or trich, which the antifungal won't touch. A test settles it.
Side-by-side comparison
| Feature | Trichomoniasis | Bacterial vaginosis | Yeast infection |
|---|---|---|---|
| Cause | Parasite (T. vaginalis) | Bacterial imbalance | Fungus (Candida) |
| STI? | Yes | Not classically; sex-associated | No |
| Odor | Fishy (sometimes) | Strong fishy, worse after sex | None |
| Discharge | Yellow-green, frothy | Thin, white or gray | Thick, white, cottage-cheese-like |
| Itch | Common | Sometimes | Often intense |
| Vaginal pH | Elevated (>4.5) | Elevated (>4.5) | Normal (<4.5) |
| First-line treatment | Oral metronidazole | Oral metronidazole or vaginal gel/cream | Antifungal (azole) cream or oral pill |
| Treat partner? | Yes | No | No |
Testing
Each condition has its own preferred test, and guessing fails. For trichomoniasis, a NAAT (nucleic acid amplification test, such as the Aptima assay) is the preferred method, with sensitivity around 95–100%, run on a vaginal swab or a female urine sample CDC, 2021. For BV, clinicians use the Amsel criteria (at least three of: thin discharge, clue cells under the microscope, vaginal pH above 4.5, and a positive fishy-odor whiff test), a Nugent score on a Gram stain, or an FDA-cleared molecular test. A yeast infection is confirmed by looking at the discharge under a microscope (a wet prep showing budding yeast or hyphae) and/or a fungal culture, with a normal vaginal pH as a supporting clue.
In practice, testing means a urine sample, a self-collected swab, or a quick exam depending on what's suspected, and it's free or low-cost at health departments, Planned Parenthood, and Title X clinics. You can get tested for trich and other STIs, and review the details on trichomoniasis testing & diagnosis. If your symptoms followed a recent new partner, also check when to test after exposure so you don't test too early to catch an infection.
Treatment compared
Because the underlying organisms differ — parasite, bacteria, fungus — the medications differ completely, and one won't cure another. Trichomoniasis is treated with the antibiotic metronidazole: women take metronidazole 500 mg orally twice daily for 7 days, while men take a single 2 g dose; tinidazole 2 g as a single dose is an alternative for either Muzny et al.. The 2021 guidelines moved women off the old single 2 g dose because the multi-day course works better. In a randomized trial about 19% of women given the single dose were still infected at follow-up versus 11% on the 7-day course.
BV is also treated with metronidazole — oral 500 mg twice daily for 7 days, or a vaginal metronidazole 0.75% gel daily for 5 days, or clindamycin 2% cream at bedtime for 7 days CDC, 2021. Standard antibiotics cure 80 to 90% of acute episodes, but BV recurs in up to 60% of women within a year, and recurrent BV (three or more episodes annually) often needs a months-long maintenance regimen rather than another single course SASGOG.
A yeast infection is treated with antifungals, not antibiotics. Uncomplicated cases respond to an intravaginal azole (such as clotrimazole or miconazole cream, many sold over the counter) or a single oral fluconazole 150 mg pill CDC, 2021. Recurrent yeast infections — four or more symptomatic episodes in a year — need a longer initial course followed by months of weekly fluconazole; stubborn cases may involve a non-albicans Candida that resists the usual fluconazole RVVC review.
Can you have more than one at once?
Yes. Co-infections happen, and trich and BV in particular travel together because both involve a disrupted vaginal environment. That makes self-treating one with an OTC product risky: you might clear one and leave the other untreated, and the symptoms won't fully resolve. A clinician can test for all three from the same visit and treat what's actually there.
There's reason to get BV sorted, too. A meta-analysis of more than 30,000 women found BV raised the risk of acquiring HIV by about 60%, because losing protective lactobacilli changes the vaginal environment Atashili et al.. Treating vaginal infections isn't only about comfort.
When to see a clinician
See a clinician if this is your first episode of these symptoms, if OTC yeast treatment didn't work within a few days, if you have a fishy odor or yellow-green discharge, if symptoms keep coming back, or if you have fever, pelvic pain, or a recent new sexual partner. Pregnancy is also a reason to get checked rather than self-treat. The faster you confirm which condition you actually have, the faster the right medication ends it.