A fishy smell from the vaginal area is most often caused by bacterial vaginosis (BV), a common condition where the balance of bacteria in the vagina shifts. It’s not always a sign of an infection you caught from someone else, and in many cases it clears up with a short course of treatment. But BV isn’t the only possibility. A handful of other conditions, habits, and even normal body changes can produce or contribute to that distinct odor.
Bacterial Vaginosis: The Most Common Cause
BV accounts for the majority of fishy vaginal odor cases. It happens when the naturally protective bacteria in the vagina, particularly species of Lactobacillus, get outnumbered by a mix of other bacteria that don’t belong there in large quantities. Those bacteria break down amino acids and produce compounds called biogenic amines, most notably cadaverine and putrescine. These are the molecules directly responsible for the fishy smell.
The process is self-reinforcing. As those amines build up, they raise the pH inside the vagina, making the environment less acidic. That shift weakens the remaining Lactobacillus colonies even further and reduces their ability to produce lactic acid, which is the vagina’s main line of defense against harmful microbes. The result is a cycle: fewer protective bacteria, more odor-causing bacteria, and a progressively stronger smell.
Along with the odor, BV typically produces a thin, milky-white or grayish discharge. Many people notice the smell is stronger after sex or during their period, both of which temporarily raise vaginal pH. BV is not a sexually transmitted infection, though sexual activity can be a trigger. It’s extremely common, affecting roughly one in three women of reproductive age at some point.
Trichomoniasis and Other Infections
Trichomoniasis, a sexually transmitted infection caused by a parasite, can produce a fishy smell that overlaps with BV. The CDC notes that trichomoniasis often causes a thin discharge that may be clear, white, yellowish, or greenish, along with itching, burning, redness, and discomfort when urinating. If you have a fishy odor paired with noticeable irritation or a colored discharge, trichomoniasis is worth considering, especially if you’ve recently had a new sexual partner.
The key difference from BV is that trichomoniasis tends to come with more inflammation. Itching and soreness are more prominent, and the discharge may look different. BV discharge is usually thin and grayish with relatively little irritation, while trichomoniasis often causes visible redness and significant discomfort. Both are treatable, but they require different approaches, so getting the right diagnosis matters.
Forgotten Tampons and Other Retained Objects
A tampon that’s been left in too long is a surprisingly common and often overlooked cause of a strong, foul vaginal odor. The smell develops as bacteria break down the trapped blood and tissue, and it can become quite intense within a few days. Other retained objects, like a broken condom or a menstrual disc that shifted out of reach, can cause the same issue.
If the odor came on suddenly, feels different from anything you’ve experienced before, and you recently used a tampon or internal menstrual product, it’s worth checking. Removing the object usually resolves the smell within a day or two. If you can’t reach it yourself, a healthcare provider can remove it quickly in the office.
Everyday Factors That Shift Your pH
Your vaginal pH naturally sits below 4.5, which is acidic enough to keep odor-causing bacteria in check. Several routine things can push that number higher and temporarily create or worsen a fishy smell:
- Semen is alkaline, with a pH around 7.2 to 8.0. Unprotected sex can raise vaginal pH for hours afterward, which is why some people notice a fishy smell specifically after intercourse.
- Menstrual blood has a higher pH than vaginal fluid. It’s normal for odor to shift slightly before and during your period.
- Lubricants and spermicides can also alter the chemical environment enough to trigger a temporary change in odor.
These shifts are usually short-lived. If the smell resolves on its own within a day or so, it’s likely just a temporary pH fluctuation rather than an infection.
Douching and Hygiene Products That Backfire
Douching is one of the most well-documented risk factors for BV and, by extension, fishy odor. It works against you by flushing out the very bacteria that keep the vagina healthy. Research consistently shows the connection: women who douche within seven days of assessment have roughly twice the odds of developing BV compared to those who don’t douche at all. One study found that participants who had douched in the previous six months had seven times the odds of reporting BV.
Scented soaps, vaginal deodorants, and perfumed wipes carry a similar risk on a smaller scale. They disrupt the microbial community and can trigger inflammation, creating exactly the conditions that allow odor-producing bacteria to thrive. The vagina is self-cleaning. Warm water on the external vulva is all that’s needed for routine hygiene.
Hormonal Changes and Menopause
Dropping estrogen levels during menopause (and sometimes during breastfeeding or certain medications) change the vaginal environment significantly. Estrogen helps maintain the thick, moist vaginal lining and supports Lactobacillus populations. When estrogen declines, the vaginal walls thin, natural lubrication decreases, and the acid balance shifts. This condition, called vaginal atrophy, can produce unusual discharge and make the tissue more vulnerable to bacterial overgrowth and odor.
A yellowish discharge is more typical of atrophy-related changes than the grayish discharge seen in BV, but the two can overlap. If you’re in perimenopause or postmenopause and noticing new vaginal odor, hormonal changes are a likely contributor.
How to Tell Normal Odor From a Problem
A healthy vagina has a smell. It’s not supposed to be odorless. Normal vaginal scent ranges from slightly tangy or sour (similar to sourdough bread) to faintly sweet or bittersweet. During your period, a metallic, copper-like smell is common and harmless. After a hard workout, sweat glands in the groin can produce a scent closer to body odor. Even a slight ammonia smell can simply mean you’re dehydrated or there’s a small amount of urine residue on the vulva.
What separates these normal variations from a problem is persistence and intensity. A distinctly fishy smell that lasts more than a day or two, gets stronger over time, or comes with discharge that looks different from your usual pattern is worth getting checked. Diagnosis is straightforward and typically involves a quick exam. A clinician looks at the discharge characteristics, checks the pH (above 4.5 suggests BV), and may examine a sample under a microscope for specific marker cells. Treatment for BV and trichomoniasis is a short course of antibiotics or antiparasitic medication, usually clearing symptoms within a week.
Reducing Your Risk of Recurrence
BV is notorious for coming back. Recurrence rates are high even after successful treatment, which makes prevention habits especially important. Using condoms or dental dams during sex limits the pH disruption caused by semen and reduces exposure to bacteria that can shift your vaginal balance. Avoiding douching and internal fragranced products removes the biggest controllable risk factor.
Probiotics containing vaginal Lactobacillus strains have generated a lot of interest, but the clinical evidence is mixed. A randomized controlled trial testing two well-studied probiotic strains (L. rhamnosus GR-1 and L. reuteri RC-14) as an add-on to standard antibiotic treatment found no improvement in cure rates at 30 or 90 days compared to antibiotics alone. Probiotics aren’t harmful, but they shouldn’t be relied on as a standalone strategy for preventing recurrence. The habits that matter most are the simple ones: skip the douche, use barrier protection, and let the vagina manage its own ecosystem.