A fishy vaginal odor is most commonly caused by bacterial vaginosis (BV), an overgrowth of certain bacteria that naturally live in the vagina. It’s extremely common, and it doesn’t mean you’re dirty or doing something wrong. The smell comes from specific chemical compounds that these bacteria produce, and in most cases, a short course of treatment clears it up.
What Creates the Fishy Smell
Your vagina naturally contains a mix of bacteria, with beneficial species keeping the environment slightly acidic (a healthy pH sits between 3.8 and 4.5). When that balance tips, odor-producing bacteria multiply and release volatile compounds called amines, specifically trimethylamine and dimethylamine. These are the same chemicals responsible for the smell of rotting fish. In more advanced imbalances, bacteria also produce compounds called putrescine and cadaverine, which intensify the odor further.
This is why the smell is often strongest after unprotected sex or during your period. Semen is alkaline, and menstrual blood raises vaginal pH. Both reduce the acidity that normally keeps those bacteria in check, temporarily amplifying amine production and making the odor more noticeable.
Bacterial Vaginosis: The Most Likely Cause
BV accounts for the vast majority of fishy vaginal odor. It’s not a sexually transmitted infection, though sexual activity can trigger it. Many people with BV have no symptoms at all beyond the smell. When symptoms do appear, they typically include:
- A thin, white or gray discharge
- A strong fishy odor, especially after sex
- Mild itching or burning around the vulva
- Burning during urination
BV is treated with antibiotics, typically a seven-day oral course or a vaginal gel or cream applied for five to seven days. The catch is that BV has a stubbornly high recurrence rate. Within 6 to 12 months of finishing antibiotics, 50% to 80% of women experience it again. This is partly because antibiotics kill the overgrown bacteria but don’t always restore the beneficial ones needed to keep the environment balanced long-term.
Other Possible Causes
Trichomoniasis
Trichomoniasis is a sexually transmitted infection caused by a parasite. It can produce a fishy smell similar to BV, but the accompanying symptoms tend to differ. Trich more commonly causes genital redness, soreness, and itching along with discomfort during urination. The discharge may be clear or white. Many people with trich have no symptoms at all, which is why it often goes undiagnosed without testing. It’s treated with a different antibiotic than BV, so getting the right diagnosis matters.
A Retained Tampon or Other Object
A forgotten tampon is more common than people think, and it produces a distinctly foul odor that gets worse over time. If the smell appeared suddenly and is particularly strong or rotten rather than just “fishy,” this is worth considering. You can sometimes feel or see the object yourself, but if you can’t reach it, a healthcare provider can remove it quickly. Tampons should be changed every 4 to 6 hours and never left in longer than 8 hours.
Trimethylaminuria (Fish Odor Syndrome)
In rare cases, a persistent fishy smell from the body, including vaginal secretions, sweat, urine, and breath, points to a genetic condition called trimethylaminuria. People with this condition lack a functioning liver enzyme that normally breaks down trimethylamine, so the compound builds up and gets released through all bodily fluids. If the fishy smell isn’t limited to your vagina and has been present most of your life, this is worth discussing with a doctor. It’s diagnosed through a urine test.
What Disrupts Your Vaginal Balance
Several everyday habits can shift the vaginal environment in ways that favor odor-producing bacteria. Douching is one of the most well-documented disruptors. Research has found that douching is independently associated with a loss of the protective, hydrogen peroxide-producing bacteria that keep the vagina healthy, while simultaneously increasing colonization by the very bacteria that cause BV. In short, douching does the opposite of what most people use it for.
Scented soaps, body washes, and feminine hygiene sprays applied inside or around the vagina have a similar effect. The vagina is self-cleaning. Warm water on the external vulva is all you need. Anything fragranced can alter pH and kill beneficial bacteria, creating the conditions for the exact odor you’re trying to prevent.
Other common triggers include new sexual partners, smoking, and prolonged antibiotic use for unrelated infections. Hormonal shifts during menopause also raise vaginal pH above 4.5, which naturally increases susceptibility to bacterial imbalance.
Restoring and Maintaining Balance
If the smell is new, persistent, or accompanied by unusual discharge, the most efficient path is getting tested. BV and trich require different treatments, and guessing wrong means the problem lingers. A provider can diagnose BV with a simple vaginal swab, often during the same visit.
For people dealing with recurrent BV, probiotics containing specific strains of Lactobacillus have shown promise. A randomized, placebo-controlled study found that taking oral capsules containing L. rhamnosus GR-1 and L. reuteri RC-14 daily for two weeks significantly improved vaginal bacterial balance compared to placebo. The improvement was substantial enough that researchers measured a meaningful shift back toward a healthy bacterial profile. These specific strains are available in over-the-counter supplements marketed for vaginal health.
Beyond probiotics, practical steps that help maintain a healthy vaginal environment include wearing cotton underwear, avoiding sitting in wet swimsuits or workout clothes for extended periods, wiping front to back, and skipping any product that introduces fragrance to the vaginal area. If you notice the smell is consistently worse after unprotected sex, using condoms can help by preventing the pH spike that semen causes.
A mild, slightly musky vaginal scent is completely normal and varies throughout your menstrual cycle. The smell worth paying attention to is a distinctly fishy one, especially if it’s accompanied by changes in discharge or any irritation. That pattern points to a treatable bacterial shift, not a hygiene problem.