The fishy smell from bacterial vaginosis typically starts improving within 2 to 3 days of beginning antibiotic treatment, with odor and discharge usually the first symptoms to clear. Without treatment, the smell can persist for weeks or months, and in some cases it won’t go away on its own at all.
What Causes the Smell
The odor isn’t caused by poor hygiene. It’s a chemical byproduct of the bacteria themselves. When the normal balance of vaginal bacteria shifts and anaerobic organisms overgrow, they produce volatile compounds called amines, specifically trimethylamine, putrescine, and cadaverine. These are the same types of compounds responsible for the smell of rotting fish. Women with high levels of the bacteria responsible for BV have dramatically elevated concentrations of these amines in vaginal fluid, while women with a healthy bacterial balance have only trace amounts.
The smell tends to be strongest after sex and during menstruation. Both semen and menstrual blood are alkaline, which raises vaginal pH and releases more of those volatile amines into the air. A healthy vaginal pH sits between 3.8 and 4.2. In BV, it rises above 4.5, creating an environment where odor-producing bacteria thrive and the smell intensifies. As long as that pH stays elevated and those bacteria remain in control, the odor continues.
How Quickly Treatment Stops the Smell
Most women notice the smell fading within 2 to 3 days of starting prescribed antibiotics. Odor and discharge tend to improve before other symptoms like irritation resolve. A standard course of treatment runs about 5 to 7 days, and by the end of it, the smell is typically gone completely.
It’s important to finish the full course even after the smell disappears. Stopping early can leave enough of the overgrown bacteria alive to rebound, bringing the odor back within days or weeks. If the smell hasn’t improved at all after a few days of treatment, that’s worth a follow-up visit, since it may indicate a different type of infection or a resistant case.
How Long It Lasts Without Treatment
Some cases of BV do resolve on their own without medication. But there’s no reliable timeline for when that happens, and many cases don’t resolve at all. The smell can persist for weeks to months in untreated BV, fluctuating in intensity but never fully clearing. It often worsens around periods and after intercourse, then fades somewhat before returning again.
Waiting it out also carries risks beyond the odor. Untreated BV raises the likelihood of contracting sexually transmitted infections and can cause complications during pregnancy. The longer the bacterial imbalance persists, the harder it can be to restore normal vaginal flora, making eventual treatment less straightforward.
Why the Smell Keeps Coming Back
Recurrence is one of the most frustrating aspects of BV. Even after successful treatment, the infection returns in a significant number of women. A 2025 clinical trial published in the New England Journal of Medicine found that 63% of women whose male sexual partners were not treated experienced a recurrence. That number dropped to 35% when partners received concurrent antibiotic treatment. Among couples where the male partner fully adhered to the treatment regimen, recurrence rates were lowest of all.
These findings support what researchers have suspected for years: BV-associated bacteria can live on a male partner’s genitalia and get passed back and forth during sex, restarting the cycle of imbalance and odor. If you’ve been treated for BV multiple times and the smell keeps returning, partner treatment is a conversation worth having with your healthcare provider.
Other factors that contribute to recurrence include douching, which disrupts vaginal pH, and having new or multiple sexual partners. Hormonal changes around menstruation can also create temporary conditions that favor the overgrowth of anaerobic bacteria.
Reducing the Smell While Waiting for Treatment to Work
During the first couple of days before antibiotics fully take effect, a few things can minimize how noticeable the odor is. Wearing breathable cotton underwear and avoiding tight clothing helps reduce moisture that can intensify the smell. Avoid douching, scented soaps, or vaginal deodorants, all of which can further disrupt pH and make the underlying problem worse.
Showering with warm water and a gentle, unscented cleanser on the external vulva is enough. The vagina is self-cleaning internally, and adding products to mask the odor almost always backfires by feeding the conditions that cause it. If the smell is noticeably stronger after sex, using condoms can help by preventing semen from raising vaginal pH.