Bacterial vaginosis (BV) produces a distinct fishy smell, often described as stale or musty. The odor tends to be strongest after sex and during your period. It’s one of the most recognizable signs of BV and is different from the mild, slightly acidic scent of healthy vaginal discharge.
Why BV Smells Fishy
The fishy odor comes from specific chemical compounds called biogenic amines, particularly putrescine, cadaverine, and trimethylamine. These are produced when certain bacteria break down amino acids in vaginal fluid. In a healthy vaginal environment, lactobacilli keep the pH acidic (below 4.5), which limits the growth of odor-producing bacteria. When BV develops, those protective bacteria are outnumbered, the pH rises above 4.5, and amine-producing bacteria flourish.
The smell gets stronger in alkaline conditions, which is why it’s more noticeable after unprotected sex (semen is alkaline) or during menstruation (blood raises vaginal pH). Clinicians actually use this chemistry to diagnose BV: adding a potassium hydroxide solution to a sample of discharge releases the amines and produces a detectable fishy odor. If you notice the smell more at those specific times, that pattern itself points toward BV rather than other infections.
What the Discharge Looks Like
BV discharge is typically thin and watery, with a greyish-white color. It coats the vaginal walls evenly rather than clumping. The volume can range from barely noticeable to enough to stain underwear. Some people notice it most after wiping, while others detect it primarily by smell. Not everyone with BV has visible discharge changes, but when they do appear, the thin, off-white consistency combined with the fishy odor is a reliable indicator.
How BV Discharge Differs From Other Infections
Three common vaginal infections produce noticeably different types of discharge, and telling them apart can help you figure out what you’re dealing with before you see a provider.
- BV: Thin, off-white or greyish discharge with a fishy odor. Usually no itching, burning, or irritation.
- Yeast infection: Thick, white, cottage cheese-like discharge. Little to no odor, but significant itching and sometimes a burning sensation.
- Trichomoniasis: Profuse, yellow-green, frothy discharge with a strong unpleasant smell (not always fishy). Often accompanied by irritation, redness, and discomfort during urination.
The key distinction is that BV is more about smell than sensation. Yeast infections itch intensely but rarely smell. Trichomoniasis tends to produce more discharge, a different color, and more physical discomfort. If you’re experiencing a fishy smell without significant itching or pain, BV is the most likely cause.
When the Smell Comes and Goes
BV odor isn’t always constant. Many people describe days where it’s barely there and other days where it’s impossible to ignore. This fluctuation tracks with pH changes throughout your menstrual cycle. Around ovulation and during your period, vaginal pH naturally shifts higher, which can intensify the amine smell. Some people first notice BV only during these windows and assume it’s normal period odor.
Sexual activity is the other major trigger. The alkaline pH of semen can release a burst of fishy odor that’s noticeable immediately after sex. If you consistently notice a strong smell after intercourse that wasn’t there before, that’s a classic BV pattern worth getting checked.
BV Tends to Come Back
One frustrating reality of BV is its recurrence rate. Between 50 and 80 percent of people who complete antibiotic treatment experience BV again within 6 to 12 months. This doesn’t mean treatment failed. BV involves a shift in the entire vaginal bacterial community, and antibiotics can clear the overgrown bacteria without fully restoring the protective lactobacilli that keep BV from returning.
If you’ve had the characteristic fishy smell resolve with treatment and then return months later, you’re in the majority. Recurrent BV is common enough that many providers will discuss longer-term management strategies rather than treating each episode as a standalone infection.