A fishy vaginal odor is almost always caused by an overgrowth of certain bacteria that produce smelly chemical compounds called amines. The most common culprit is bacterial vaginosis (BV), which affects roughly one in three women of reproductive age at some point. The good news: it’s treatable, and there are concrete steps you can take to clear it up and keep it from coming back.
What Actually Causes the Smell
Your vagina naturally contains a community of bacteria, dominated by protective species called lactobacilli. These bacteria keep the environment acidic (a healthy pH sits between 3.8 and 4.5), which prevents harmful organisms from thriving. When that balance tips, anaerobic bacteria multiply and start breaking down amino acids into compounds like putrescine, cadaverine, and trimethylamine. These are the chemicals responsible for the fishy odor.
The smell often gets stronger after sex because semen is alkaline, which triggers the release of more of those amines. It can also intensify during your period for similar pH-related reasons.
BV vs. Other Infections
Bacterial vaginosis is the most likely cause, but it’s not the only one. Trichomoniasis, a sexually transmitted infection caused by a parasite, can also produce a fishy smell. Knowing the difference matters because the treatments aren’t the same.
- Bacterial vaginosis: Thin, white or gray discharge. Fishy odor, especially after sex. May include mild itching or burning during urination. Many women have no symptoms at all beyond the smell.
- Trichomoniasis: Discharge can be clear, white, yellowish, or greenish with a fishy smell. More likely to cause redness, soreness, and genital irritation. Discomfort during urination is common.
A forgotten tampon, though less common, can also produce a strong fishy odor. If you suspect this, gently check and remove it, then monitor for any signs of infection over the next day or two.
At-Home pH Testing
Over-the-counter vaginal pH test strips can give you a useful first clue. A reading at or below 4.5 is generally normal. A reading above 4.5 suggests BV or trichomoniasis. A yeast infection, by contrast, typically doesn’t change your pH much at all. These kits won’t give you a definitive diagnosis, but they can help you decide whether what you’re dealing with needs a clinical visit or might resolve on its own.
Medical Treatment
If the fishy smell persists for more than a few days, a course of antibiotics is the most reliable fix. The standard options are oral metronidazole taken twice a day for seven days or a vaginal antibiotic gel or cream applied for five to seven days. Both approaches are effective at clearing the bacterial overgrowth and eliminating the odor, usually within a few days of starting treatment.
Here’s the frustrating part: BV has one of the highest recurrence rates of any common infection. Studies tracking women after antibiotic treatment found that 69 to 80% experienced a return of BV within 12 months. That’s why treatment alone isn’t enough. Prevention habits matter just as much as the initial fix.
Boric Acid Suppositories
Boric acid vaginal suppositories have become a popular option, particularly for recurrent BV. Clinicians typically prescribe a daily suppository for 7 to 14 days as an initial phase, then transition to using one two to three times per week for ongoing maintenance. In clinical data, about 77% of women reported satisfaction with the regimen, and side effects were uncommon, mostly limited to mild irritation or leaking. Some women used boric acid safely over several years.
Boric acid is available over the counter, but it’s worth noting that it’s a supplement rather than an FDA-approved drug. If you’re pregnant, don’t use it. And it should only ever be used vaginally, never taken by mouth.
Probiotics for Vaginal Health
Since the root problem is a disrupted bacterial community, restoring protective lactobacilli makes logical sense. The most studied probiotic strains for vaginal health include L. rhamnosus, L. reuteri, L. crispatus, and L. paracasei. These have been tested both as oral supplements and vaginal formulations. Earlier clinical trials using L. rhamnosus GR-1 and L. reuteri RC-14 showed notable improvement in vaginal flora, though more recent trials with the same strains have had mixed results.
Probiotics work best as a complement to antibiotic treatment rather than a replacement. Taking them during or after a course of antibiotics may help reestablish a healthy bacterial balance and reduce the odds of recurrence.
Habits That Help (and Ones That Hurt)
Douching is the single most counterproductive thing you can do. It strips away protective bacteria, raises vaginal pH, and directly increases your risk of BV. Your vagina is self-cleaning. Warm water on the external vulva is all you need. Scented soaps, washes, sprays, and wipes marketed for vaginal freshness can cause the same disruption.
Other habits that reduce your risk:
- Condom use: Semen shifts vaginal pH and introduces new bacteria. Consistent condom use with new or multiple partners significantly lowers BV risk.
- Cotton underwear and breathable clothing: Moisture and heat create a friendlier environment for anaerobic bacteria. Switching to cotton and avoiding tight synthetic fabrics helps keep things dry.
- Wiping front to back: Some of the bacteria that produce fishy-smelling amines, particularly E. coli strains, naturally live in the intestinal tract. Front-to-back wiping prevents transferring them forward.
Diet and Your Vaginal Microbiome
This connection is less intuitive, but emerging evidence suggests your diet influences which bacteria dominate your vaginal environment. Research on dietary quality found that higher carbohydrate intake was associated with greater abundance of L. crispatus, one of the most protective vaginal bacteria. Lower-quality diets correlated with higher levels of Gardnerella vaginalis and Atopobium vaginae, both of which are linked to BV.
The mechanism likely involves glycogen, a carbohydrate stored in vaginal tissue that lactobacilli feed on. A diet with adequate complex carbohydrates may support glycogen production, giving protective bacteria more fuel. Overall dietary quality, measured by how closely someone followed general healthy eating guidelines, showed a similar pattern: better diets meant more beneficial bacteria. This doesn’t mean loading up on sugar. It means a balanced diet with whole grains, fruits, and vegetables may support vaginal health in ways that go beyond general wellness.
When the Smell Keeps Coming Back
If you’ve been treated for BV and the fishy smell returns within weeks or months, you’re dealing with recurrent BV, which is genuinely common given the 69 to 80% recurrence rate. At this point, a maintenance strategy becomes important. This might involve periodic boric acid suppositories, a longer or repeated course of antibiotics, probiotics, or some combination of all three. Some clinicians recommend a maintenance antibiotic gel used twice weekly after the initial treatment course to suppress recurrence.
It also helps to look at the contributing factors. A new sexual partner, inconsistent condom use, or douching can retrigger the cycle. If you have a regular male partner, some researchers believe the bacteria can be shared back and forth, though treatment of male partners isn’t yet standard practice. Tracking your symptoms alongside your cycle, sexual activity, and hygiene habits can reveal patterns that make prevention more targeted.