A fishy smell from your vagina is almost always caused by an overgrowth of certain bacteria that produce odor-causing compounds. The most common culprit is bacterial vaginosis (BV), the single most frequent vaginal condition in women ages 15 to 44. It’s not a sign of poor hygiene, and it’s very treatable once you know what’s going on.
What Causes the Fishy Smell
Your vagina naturally contains a mix of bacteria, with beneficial species keeping the environment slightly acidic (a normal pH of 3.8 to 4.5). When that balance shifts and certain anaerobic bacteria multiply, they break down amino acids and other compounds into chemicals called biogenic amines. Three of these are the main offenders behind the fishy smell: putrescine, cadaverine, and trimethylamine. The names alone tell you something about how they smell.
These bacteria thrive when the vaginal pH rises above 4.5, becoming less acidic. Once that happens, the protective bacteria lose their advantage and odor-producing species take over. This is why the smell often gets stronger after sex or during your period, both of which temporarily raise vaginal pH.
Bacterial Vaginosis: The Most Likely Cause
BV is responsible for the fishy smell in the majority of cases. It’s not a sexually transmitted infection, though sexual activity can trigger it. Many people with BV notice a thin, white or grayish discharge with a strong fish-like odor, especially after sex. Others have no symptoms at all and only discover it during a routine exam.
What makes BV tricky is that it tends to come back. The bacterial imbalance can recur even after successful treatment, particularly if the factors that disrupted the environment in the first place haven’t changed. Left untreated, BV can increase your risk of pelvic inflammatory disease, which can affect fertility, and it raises susceptibility to sexually transmitted infections.
Other Possible Causes
Trichomoniasis, a common sexually transmitted infection caused by a parasite, can also produce a fishy odor. The discharge may look clear or white and can be frothy or yellowish-green. Many people with trichomoniasis also experience itching, burning, or irritation that BV doesn’t typically cause. If your fishy smell comes with significant discomfort, trichomoniasis is worth considering.
A forgotten tampon or other retained object can produce a strong, foul smell that may seem fishy. This is usually more pungent than BV and resolves quickly once the object is removed.
Yeast infections, on the other hand, are generally not the cause of a fishy smell. They tend to produce a mild, slightly sour or bread-like odor, if any odor at all. The hallmark of a yeast infection is thick, white, cottage cheese-like discharge with itching, which is quite different from the thin, fishy-smelling discharge of BV.
How BV Is Diagnosed and Treated
Diagnosis is straightforward. A healthcare provider looks for a combination of signs: thin, milky discharge that coats the vaginal walls, a pH above 4.5, the presence of “clue cells” (vaginal cells covered in bacteria visible under a microscope), and a fishy odor. Meeting three of these four criteria confirms the diagnosis.
Treatment typically involves a course of antibiotics, either taken orally or applied vaginally as a gel or cream. Most people notice the smell resolve within a few days of starting treatment. The full course usually lasts about a week, and it’s important to finish it even if symptoms clear up sooner.
Why It Keeps Coming Back
Recurrence is one of the most frustrating aspects of BV. The same bacterial imbalance can return weeks or months after treatment, sometimes repeatedly. Several factors contribute to this cycle.
Douching is one of the biggest risk factors. It disrupts the natural bacterial community, causes inflammation, and gives harmful bacteria an opportunity to take hold. Research has found that women who use feminine washes or gels have roughly 3.5 times the odds of developing BV compared to those who don’t. Vaginal douches are consistently linked to bacterial imbalance and are not recommended by any major medical organization.
Some intimate hygiene products are directly harmful to protective bacteria. In lab studies, certain vaginal moisturizers completely killed off beneficial Lactobacillus bacteria within 24 hours. Scented soaps, sprays, and wipes can have similar effects. The vagina is self-cleaning, and warm water on the external area is all you need.
Reducing Your Risk
Keeping your vaginal environment stable is the most effective prevention strategy. That means avoiding douching, scented products near the vagina, and unnecessary internal washing. Wearing breathable cotton underwear and changing out of wet swimsuits or sweaty workout clothes promptly can also help.
Probiotics show genuine promise for preventing recurrence. In a clinical trial of 120 women with a history of recurring BV, those who used vaginal probiotic capsules containing Lactobacillus strains had a recurrence rate of just 16%, compared to 45% in the placebo group. The protective effect lasted through 11 months of follow-up. While more research is ongoing, vaginal probiotics appear to be a safe, well-tolerated option worth discussing with your provider if BV keeps returning.
Using condoms during sex can help maintain vaginal pH, since semen is alkaline and temporarily shifts the environment in a direction that favors odor-producing bacteria. If you notice the smell consistently worsens after unprotected sex, this is likely why.
What a Normal Vagina Smells Like
Every vagina has a natural scent, and it changes throughout your menstrual cycle. A mild, slightly tangy or musky smell is completely normal and comes from the same Lactobacillus bacteria that keep the environment healthy. The smell can shift slightly before your period, after exercise, or depending on what you’ve eaten. None of this is cause for concern.
The smell that warrants attention is distinctly fishy, persistent, or accompanied by unusual discharge. A sudden change in odor, especially paired with itching, burning, or a change in discharge color or consistency, is your body signaling that the bacterial balance has shifted and it’s time to get checked.