Two of the most common causes of an unusual vaginal discharge are a yeast infection and bacterial vaginosis (BV). Yeast tends to bring thick, white, odorless discharge with itching, while BV brings a thin white-to-gray discharge with a fishy smell. The overlap is real, and only a test reliably tells them apart.
thick white discharge, intense itch (not an STI)
thin grey discharge, fishy odor (not an STI)
| Item | Value |
|---|---|
| Vaginal yeast infection (candidiasis) | curable — thick white discharge, intense itch (not an STI) |
| Bacterial vaginosis (BV) | curable — thin grey discharge, fishy odor (not an STI) |
Quick answer: what's most likely behind your discharge
If your discharge changed and you're trying to name the cause, the list is short. The two heavyweights are vaginal yeast infection (candidiasis) and bacterial vaginosis (BV), and despite being lumped together with sexually transmitted infections, neither is a classic STI. Yeast is a fungal overgrowth, not something you usually catch from a partner, and BV is a shift in your own bacteria rather than an organism passed during sex. Some STIs (like trichomoniasis or gonorrhea) can also change discharge, so guessing from color and smell alone is risky.
These conditions overlap too much to separate by sight, and several can be completely silent. The symptom points you in a direction; a test settles it.
The two leading causes, explained
Vaginal yeast infection (candidiasis)
A vaginal yeast infection is a fungal overgrowth, usually caused by Candida albicans, a yeast that already lives on the body in small amounts. When the local balance tips in its favor, it multiplies and inflames the vaginal tissue. It's one of the most common fungal infections and is not usually acquired through sex, so it isn't classed as an STI CDC, candidiasis.
The tell-tale pattern is itching or soreness paired with a discharge that's often thick and white. Many people describe it as cottage-cheese-like, without a strong odor. You may also notice pain during sex or a burning sensation when you urinate. Most cases are mild, but a severe one can bring redness, swelling, and even small cracks in the vaginal wall CDC, signs & symptoms. For the full picture of what to look for, see our guide to yeast infection symptoms.
Bacterial vaginosis (BV)
BV is an imbalance rather than a single invading germ. The protective Lactobacillus bacteria that normally dominate the vagina get crowded out by anaerobic bacteria, and that shift changes how the discharge looks and smells. It's the most common vaginal condition in women ages 15–44 CDC, about BV.
The classic signature is a thin, white or gray discharge plus a strong fish-like odor, often more noticeable after sex because semen raises vaginal pH and amplifies the smell. Some people also get itching, burning, or discomfort while urinating. Many people with BV have no symptoms at all, which is one reason it goes undiagnosed. Our overview of bv symptoms walks through the variations.
How to tell them apart
There are a handful of discriminating features clinicians lean on. None is perfect on its own, but together they shape the suspicion before a test confirms it:
- Odor is the most useful clue at home. A strong fishy smell, especially right after sex, points toward BV. Yeast is typically odorless or only faintly yeasty.
- Texture and color. Yeast discharge is usually thick and white, like cottage cheese. BV discharge is thin and runs white to gray.
- The dominant symptom. Intense itching and soreness skew toward yeast. BV is more about odor and a change in discharge than relentless itch, though burning can occur with either.
- Vaginal pH is the quiet tie-breaker. Yeast leaves pH normal (under 4.5), while BV pushes it higher (above 4.5). It's the single most discriminating feature, and it's the basis of the home-test strips you can buy. A normal pH with itching leans yeast, an elevated pH with odor leans BV.
Even with all four lined up, the patterns blur. A pH strip can hint at BV but won't rule out a co-existing infection or a true STI, and itching shows up in both. Overlapping symptoms are why you usually can't self-diagnose this. A test is what turns a guess into an answer.
Yeast vs BV: side-by-side comparison
| Feature | Yeast infection (candidiasis) | Bacterial vaginosis (BV) |
|---|---|---|
| Underlying cause | Overgrowth of Candida yeast (fungal) | Loss of Lactobacillus, overgrowth of anaerobic bacteria |
| Is it an STI? | No — not usually sexually acquired | No — an imbalance, not a transmitted germ |
| Discharge | Thick, white, often cottage-cheese-like | Thin, white to gray |
| Odor | None or faintly yeasty | Strong, fishy — worse after sex |
| Main symptom | Itching and soreness | Odor and changed discharge; often no symptoms |
| Vaginal pH | Normal (under 4.5) | Elevated (above 4.5) |
| How it's confirmed | Wet prep / KOH microscopy or fungal culture | Amsel criteria, Nugent score, or molecular test |
How it's tested
Yeast is diagnosed by looking at the discharge under a microscope, a wet prep with saline or 10% KOH that shows budding yeast, hyphae, or pseudohyphae, and sometimes a fungal culture; vaginal pH stays normal CDC tx guidelines, 2021. BV is diagnosed by Amsel criteria (three or more of: thin discharge, clue cells on microscopy, pH above 4.5, and a positive whiff test), by the Nugent score on a Gram stain (the reference standard), or by an FDA-cleared molecular test CDC BV guidelines, 2021. In practice that means a quick exam, a self-collected swab, or sometimes a urine sample depending on what's suspected, often free or low-cost at health departments, Planned Parenthood, and Title X clinics, with results usually back in a few days. See exactly how to get tested, and if a partner exposure is on your mind, check when to test after exposure.
What to do next
Don't reach for a leftover antifungal on a hunch. Treating the wrong condition delays relief and can muddy a later test. If symptoms are new, recurrent, or don't match the textbook yeast picture, get a clinician to confirm what it actually is. Once you have an answer, treatment is straightforward and targeted, and a partner check may be worth discussing for some causes.
Red flags — when to get seen urgently
Most discharge changes are not emergencies, but a few signs warrant prompt care rather than waiting it out:
- Fever, chills, or lower abdominal or pelvic pain, which can signal an infection spreading beyond the vagina.
- Discharge that's green, yellow, frothy, or foul-smelling in a way that doesn't fit either pattern, which can point to a true STI like trichomoniasis or gonorrhea.
- Severe swelling, raw cracks in the vaginal wall, or pain that keeps you from urinating.
- You're pregnant, since untreated BV in pregnancy carries risks worth addressing with a clinician.
- Symptoms that keep coming back after treatment, which deserve a fresh look rather than another round of guesswork.