Vaginal odor is normal, and every vagina has a natural scent. But when that scent changes noticeably or becomes unpleasant, it usually signals a shift in the balance of bacteria that keep things healthy down there. The most common cause of a strong or “fishy” vaginal smell is bacterial vaginosis, though sweat, hormonal changes, infections, and even a forgotten tampon can all play a role.
What “Normal” Smells Like
A healthy vagina is home to billions of beneficial bacteria that maintain an acidic environment, with a pH between 3.8 and 4.5. That acidity is what keeps harmful organisms in check, and it also gives the vagina a mild, slightly tangy scent. This smell can shift throughout your menstrual cycle, after exercise, or after sex, and none of that is cause for concern.
What you’re looking for is a change from your own baseline. If you’ve always had a faint smell and it suddenly becomes strong, persistent, or fishy, something has likely disrupted the bacterial balance inside the vagina or on the surrounding skin.
Bacterial Vaginosis: The Most Common Cause
Bacterial vaginosis (BV) is responsible for the majority of cases where vaginal odor becomes noticeably fishy. It happens when the beneficial bacteria lose ground to other organisms, raising the vaginal pH above 4.5 and triggering the production of specific chemicals called volatile amines. The two main culprits behind the smell are trimethylamine and dimethylamine. In more severe cases, compounds called putrescine and cadaverine build up in vaginal fluid at high concentrations, and yes, those chemicals are exactly as unpleasant as their names suggest.
BV typically produces a thin, grayish-white discharge with a fishy odor that tends to get stronger after sex and during your period. You might not have any itching or irritation at all, which is one reason people sometimes dismiss it or assume the smell is just “them.” BV isn’t a sexually transmitted infection, but sex can trigger it by temporarily raising vaginal pH. It can also develop after douching, using scented products, or for no obvious reason at all.
BV is treatable and usually clears up with a short course of prescription medication. Leaving it untreated, however, raises the risk of other complications, so it’s worth getting checked.
Sweat and External Odor
Sometimes the smell isn’t coming from inside the vagina at all. Your groin has a high concentration of apocrine sweat glands, the same type found in your armpits. These glands produce sweat that’s thicker and richer in fat and protein than the sweat on your arms or legs. The sweat itself is odorless, but when it meets the bacteria living on your skin, it breaks down and produces a strong, musky smell.
That smell can get trapped in skin folds and mix with your vagina’s natural scent, creating something much more pungent than either would be on its own. Tight clothing, synthetic underwear, and long stretches without showering all make this worse. If the smell fades after a shower and doesn’t come with unusual discharge, external sweat is the likely explanation. Wearing breathable cotton underwear and washing the vulva (the outer area) with plain water or a mild, unscented soap is usually enough to manage it.
Trichomoniasis and Other Infections
Trichomoniasis is a sexually transmitted infection caused by a parasite, and it can produce a fishy smell that overlaps with BV. The key difference is the discharge: trichomoniasis often causes a thin discharge that’s yellowish or greenish, sometimes frothy, and frequently comes with itching, burning, or irritation during urination. Many people with trichomoniasis have no symptoms at all, so a new partner or unprotected sex in your recent history is worth mentioning to a healthcare provider if you’re dealing with a persistent smell.
Yeast infections, by contrast, don’t usually cause a strong odor. They’re more associated with thick, white, cottage cheese-like discharge and intense itching. If smell is your primary concern, yeast is less likely to be the cause.
Forgotten Tampons and Retained Objects
This is more common than most people realize, and the smell is unmistakable. A tampon left in place for more than eight hours begins to harbor bacteria that produce an intensely foul odor, often described as rotten. It can happen easily: you insert a new tampon without removing the old one, or you forget about one at the end of your period. The longer it stays, the worse the smell gets, and it can eventually lead to bacterial vaginosis or, in rare cases, toxic shock syndrome.
If you notice a sudden, overwhelmingly bad smell and can’t identify a cause, it’s worth checking whether something has been left inside. A healthcare provider can remove it quickly and safely if you can’t reach it yourself.
Hormonal Shifts That Change Your Scent
Your vaginal pH fluctuates throughout the month. During menstruation, blood raises the pH temporarily, which can change how you smell. Ovulation, pregnancy, breastfeeding, and menopause all shift hormone levels in ways that alter the vaginal environment. These changes are normal, but they can make you more susceptible to BV or other imbalances, especially during periods when estrogen drops and the beneficial bacteria have less support.
If you’ve noticed the smell correlates with a specific point in your cycle and it resolves on its own within a day or two, hormonal fluctuation is the most likely explanation.
What Makes Odor Worse
Douching is one of the most counterproductive things you can do. It feels like a logical fix, but it strips away the protective bacteria and raises your risk of BV. Women who douche at least once a month have a 1.4 times higher risk of developing bacterial vaginosis compared to those who don’t. Douching within the past week raises that risk to 2.1 times. Scented soaps, sprays, wipes, and deodorants marketed for the vaginal area cause similar disruption. The vagina is self-cleaning; adding products to the internal environment almost always makes odor problems worse, not better.
Signs That Need Medical Attention
Some odor changes resolve on their own, especially those tied to sweat, diet, or your menstrual cycle. Others need treatment. You should see a healthcare provider if you notice a persistent fishy or foul smell that doesn’t go away after showering, especially if it comes with discharge that’s an unusual color or consistency. Itching, burning during urination, pelvic pain, fever, or chills alongside odor are all signals that something more than a minor imbalance is going on.
If you’ve recently had a new sexual partner, or if you’ve tried over-the-counter yeast treatments without improvement, those are also reasons to get an exam. Providers can check your vaginal pH and look at a sample under a microscope to identify whether BV, trichomoniasis, or another condition is responsible, and treatment is typically straightforward once the cause is clear.