A fishy smell from the vagina is almost always caused by an overgrowth of certain bacteria, a condition called bacterial vaginosis (BV). It’s extremely common, and it’s treatable. The smell comes from specific compounds, cadaverine and putrescine, that are produced when anaerobic bacteria overtake the protective bacteria that normally keep the vagina acidic and healthy. Getting rid of the odor means restoring that bacterial balance, and in most cases you’ll need a short course of prescription antibiotics to do it.
Why It Smells Fishy
A healthy vagina is home to large populations of Lactobacillus bacteria, which produce lactic acid and keep the vaginal pH between 3.8 and 4.5. About 30% of women at any given time have a vaginal microbiome where these protective bacteria are depleted and replaced by a mix of anaerobic bacteria, including Gardnerella vaginalis and Prevotella species. These bacteria break down amino acids and produce compounds called biogenic amines, particularly cadaverine and putrescine, which are responsible for the characteristic fishy smell.
The odor often becomes stronger after sex because semen is alkaline, which raises vaginal pH and releases more of those amines into the air. You might also notice a thin white or gray discharge, mild itching, or burning during urination. Many women with BV have no symptoms other than the smell.
Other Possible Causes
BV is the most common reason for a fishy odor, but it’s not the only one. Trichomoniasis, a sexually transmitted infection caused by a parasite, can produce a similar fishy smell along with a clear or white discharge. Trichomoniasis tends to cause more redness, soreness, and irritation than BV, and it requires a different treatment. A healthcare provider can distinguish between the two with a simple exam or swab test.
External odor from sweat is a different issue entirely. The vulvar area has apocrine sweat glands (the same type found in your armpits), and trapped sweat can create a musky or sour smell. This kind of odor is on the skin surface and washes away with water. If the smell is clearly coming from discharge rather than skin, it’s more likely BV or another internal issue.
Prescription Treatment
The standard treatment for BV is a seven-day course of oral antibiotics, typically taken twice daily. There are also vaginal options: an antibiotic gel applied once daily for five days, or an antibiotic cream used at bedtime for seven days. A single-dose oral treatment also exists as an alternative. All of these have similar cure rates, and your provider will help you choose based on your preferences and medical history.
Most women notice the odor starting to fade within two to three days of beginning treatment. It’s important to finish the full course even if symptoms disappear early, because stopping too soon increases the chance of the bacteria bouncing back.
Why It Keeps Coming Back
BV is notorious for recurring. Many women experience three or more episodes per year. This happens because the anaerobic bacteria can persist in a protective film even after antibiotic treatment, and the Lactobacillus population doesn’t always recover quickly enough to maintain an acidic environment. For recurrent cases, providers sometimes prescribe a longer course of treatment or a maintenance regimen using vaginal antibiotic gel applied a few times per week after the initial treatment ends.
Certain habits raise your risk of recurrence. Douching is one of the biggest contributors. It strips away protective bacteria and raises vaginal pH, creating the exact conditions that allow BV-causing bacteria to thrive. Women who douche at least once a month have a 1.4 times higher risk of developing BV, and those who douched within the past week have roughly double the risk. The vagina is self-cleaning, and water on the external vulva during a shower is all that’s needed.
What You Can Do at Home
If you have a mild fishy odor and no other symptoms, a few changes may help before the situation progresses:
- Stop douching. This is the single most impactful habit to change. Internal rinsing with water, vinegar, or commercial products disrupts the vaginal ecosystem.
- Avoid scented products. Fragranced soaps, body washes, sprays, and wipes in the vulvar area can irritate tissue and shift pH.
- Wear breathable underwear. Cotton or moisture-wicking fabrics help reduce trapped moisture that encourages bacterial overgrowth.
- Change out of sweaty clothes promptly. Sitting in damp workout clothing creates a warm, moist environment that favors anaerobic bacteria.
Boric acid vaginal suppositories are sometimes used as an add-on treatment, particularly for recurrent BV. They work by lowering vaginal pH, making the environment less hospitable to the bacteria that cause odor. They’re available over the counter but should be used at bedtime and never taken by mouth. Boric acid can weaken condoms and diaphragms, so barrier contraception isn’t reliable during use. If symptoms don’t improve within a few days, the next step is a prescription.
Probiotics for Vaginal Health
Oral probiotics containing specific Lactobacillus strains can help restore the vaginal microbiome, though they work best as a complement to antibiotic treatment rather than a replacement. In a clinical study, women who took a daily oral probiotic containing Lactobacillus acidophilus, Lactobacillus rhamnosus, and Lactobacillus reuteri for six weeks showed significant improvement. Among those who started with disrupted vaginal flora, 60% returned to a healthy bacterial balance after the probiotic course, with measurable increases in Lactobacillus colonization in the vagina.
These bacteria produce lactic acid, which lowers pH and creates antimicrobial conditions that make it harder for odor-causing bacteria to survive. Look for products that contain at least 10 billion colony-forming units and list specific Lactobacillus strains on the label. Probiotics aren’t a quick fix for an active infection, but they can help reduce the likelihood of BV returning after antibiotic treatment.
How to Tell If It’s Something Else
Not every vaginal odor signals BV. A yeast infection can change how things smell slightly, but the hallmark symptoms are intense itching and a thick, white, cottage cheese-like discharge, not a fishy odor. Sweat-related odor from the vulvar skin smells more musky or sour and improves with a shower. An ammonia-like smell can come from urine residue on underwear, particularly if you experience any degree of incontinence.
A fishy smell that persists for more than a few days, comes with unusual discharge, or gets stronger after sex is worth getting checked. A provider can confirm BV with a simple test that checks vaginal pH (above 4.5 points toward BV) and looks at a sample under a microscope. The visit is quick, the diagnosis is straightforward, and treatment typically resolves the odor within a week.