A fishy smell from your genitals is most commonly caused by bacterial vaginosis (BV), a condition where the natural balance of bacteria in the vagina shifts. Instead of the protective bacteria that normally dominate, certain anaerobic bacteria overgrow and produce a chemical called trimethylamine, the same compound responsible for the smell of rotting fish. BV is extremely common and not a sexually transmitted infection, though sexual activity can trigger it.
What Creates the Fishy Smell
A healthy vagina is home to large numbers of Lactobacillus bacteria, which keep the environment slightly acidic (below a pH of 4.5) and crowd out harmful organisms. When that balance tips, anaerobic bacteria like Gardnerella and Mobiluncus begin to dominate. These bacteria break down a compound naturally present in vaginal fluid into trimethylamine, and that’s what you’re smelling. The odor is often strongest after sex or during your period, because semen and menstrual blood are both alkaline, which temporarily raises vaginal pH and releases more trimethylamine into the air.
BV vs. Other Infections
BV is the most likely explanation for a fishy odor, but it’s not the only one. Trichomoniasis, a sexually transmitted parasite, can also produce a fishy smell. Knowing which you’re dealing with matters because the treatments differ.
- Bacterial vaginosis typically causes a thin, white or gray discharge with a strong fishy odor. You might have mild itching around the outside of the vagina, but many people with BV have no discomfort beyond the smell.
- Trichomoniasis is more inflammatory. It causes itching, burning, redness, and soreness of the genitals, sometimes with a frothy, yellow-green discharge. The fishy smell can be present but is usually accompanied by noticeable irritation that BV doesn’t cause.
If you have significant redness, soreness, or a greenish discharge alongside the odor, trichomoniasis is worth considering. A simple swab test at a clinic can distinguish between the two.
Hygiene Products Often Make It Worse
If your instinct is to wash the smell away with feminine washes or douches, that approach backfires. These products are one of the strongest risk factors for developing BV in the first place.
Vaginal douching within the previous week is associated with a 44% decrease in Lactobacillus detection, meaning it kills off the very bacteria keeping your vagina healthy. The more frequently you douche, the greater the damage to hydrogen peroxide-producing Lactobacillus strains, which are especially important for maintaining a protective acidic environment. Women who douched in the previous six months had seven times the odds of reporting BV compared to those who never douched.
Feminine washes and gels carry similar risks. One study found that women using feminine washes had 3.5 times the odds of reporting BV compared to those who didn’t use them. Lab testing showed that some popular products, including Vagisil, completely killed Lactobacillus bacteria within 24 hours of exposure. Overall, women who used any feminine hygiene product had three times the odds of reporting conditions like BV, urinary tract infections, or STIs.
The vagina is self-cleaning. Warm water on the external vulva is all that’s needed. Soap on the outer skin is fine, but nothing should go inside the vaginal canal.
How BV Is Diagnosed and Treated
Diagnosis is straightforward. A healthcare provider checks whether the vaginal pH has risen above 4.5, examines the discharge, and may look at a sample under a microscope to identify the characteristic “clue cells” of BV. At least three clinical signs need to be present for a formal diagnosis.
Treatment is a short course of antibiotics, typically taken orally or applied as a vaginal gel for about a week. Most people notice the smell improving within a few days of starting treatment. The frustrating part is recurrence: BV comes back within a few months in a significant number of people, sometimes because the underlying shift in vaginal bacteria was never fully corrected.
Restoring Healthy Vaginal Bacteria
Because BV is fundamentally a problem of bacterial imbalance, there’s growing interest in using probiotics to help restore Lactobacillus populations. Several Lactobacillus strains isolated from the vaginal ecology of healthy women have shown activity against BV-causing bacteria in lab studies. Lactobacillus crispatus, one of the dominant species in a healthy vagina, has been shown to reduce discharge and irritation when administered orally or vaginally. Lactobacillus reuteri has reduced bacterial burden and tissue inflammation in animal models of vaginal infection.
Probiotics aren’t a replacement for antibiotics when you have active BV, but they may help prevent recurrence after treatment. Look for products specifically formulated for vaginal health containing L. crispatus or L. rhamnosus, as these have the most supporting evidence. General gut-health probiotics won’t necessarily contain the right strains.
Less Common Causes Worth Knowing
If the fishy smell isn’t limited to your genitals and also comes from your sweat, breath, or urine, a rare metabolic condition called trimethylaminuria (sometimes called fish odor syndrome) could be responsible. In this condition, the body can’t properly break down trimethylamine, the same chemical that causes the smell in BV. Instead of being converted to an odorless form, it builds up and seeps out through sweat, saliva, and urine, creating a persistent fishy odor across the whole body.
Trimethylaminuria can be genetic, meaning the enzyme responsible for processing trimethylamine doesn’t work properly from birth. It can also develop later in life from liver disease, an imbalanced gut microbiome, or from taking high doses of choline or carnitine supplements. If the smell is widespread rather than localized, this is worth raising with your doctor.
What a Normal Vagina Smells Like
Every vagina has a scent, and that’s completely normal. A mild, slightly tangy or musky smell reflects the acidic environment maintained by healthy Lactobacillus bacteria. This smell changes throughout your menstrual cycle, after exercise, and depending on what you’ve eaten. None of that is a problem. The concern is specifically a strong fishy odor, which signals that the bacterial balance has shifted and anaerobic bacteria are producing trimethylamine. If that’s what you’re experiencing, it’s one of the most treatable conditions in gynecology, and getting it checked sooner rather than later prevents it from recurring or leading to secondary issues like urinary tract infections.