It happens. You’re sitting at your desk, or maybe you’re at the gym, and suddenly you catch a whiff of something that definitely wasn't there yesterday. It’s distinct. It’s pungent. It’s unmistakably fishy.
Don't panic. Honestly, most women deal with this at least once, and it doesn't mean you’re "dirty" or that your body is permanently broken. But it is your body’s way of sending a flare-up. If you're asking why does my vagina smell fishy, you’re usually looking at a chemistry problem, not a hygiene problem. In fact, trying to scrub the smell away with harsh soaps is often the fastest way to make the whole situation ten times worse.
The vagina is a self-cleaning oven. It’s a delicate ecosystem of bacteria—mostly Lactobacillus—that keeps the pH levels slightly acidic, usually between 3.8 and 4.5. When that balance gets hijacked, things start to smell.
The most likely culprit: Bacterial Vaginosis (BV)
If we’re betting on the most common cause, it’s Bacterial Vaginosis. BV isn't technically an infection you "catch" from someone else like a cold; it’s an overgrowth. Specifically, the "good" bacteria get outnumbered by anaerobic bacteria like Gardnerella vaginalis.
Why does this cause a fishy smell? It’s actually chemistry. When these anaerobic bacteria break down proteins, they produce compounds called amines (like trimethylamine). These are the exact same compounds that make old fish smell like, well, old fish.
The smell often gets noticeably stronger after sex. Semen is alkaline. When it hits the acidic environment of the vagina, it triggers a chemical reaction that releases those amines into the air. If you notice a "fishy flash" right after intercourse, BV is almost certainly the reason. You might also notice a thin, grayish-white discharge. Sometimes there's itching, but often, the smell is the only real symptom.
It could also be Trichomoniasis
While BV is an imbalance, Trichomoniasis (or "Trich") is an actual parasite. It's a very common sexually transmitted infection caused by Trichomonas vaginalis.
Trich can mimic BV because it also produces a foul, fishy odor. However, the discharge is usually a bit different—often greenish-yellow and sometimes frothy. It also tends to hurt more. You might feel a stinging sensation when you pee or significant redness and irritation around the vulva. According to the CDC, about 70% of people with Trich don't have any symptoms at all, but when they do, the odor is a primary red flag.
The "forgotten" factor
Let's talk about the thing nobody wants to admit: the forgotten tampon.
It sounds impossible. How could you forget? But it happens to the best of us, especially at the end of a period when the flow is light. A tampon left in for several days creates a breeding ground for bacteria. The resulting smell isn't just fishy; it’s usually described as "deathly" or "rotting." It is incredibly pungent.
If you suspect this, reach in and check. If you find one and can't get it out, or if you feel feverish after removing it, get to an urgent care immediately. While rare, Toxic Shock Syndrome (TSS) is still a risk, and the bacterial load from a retained foreign object is no joke.
Why your "hygiene" routine might be the problem
Here is the irony. Many people, when they first notice a slight change in scent, reach for the scented wipes, the vaginal deodorants, or—heaven forbid—a douche.
Stop.
Douching is arguably the worst thing you can do for vaginal health. It flushes out the Lactobacillus (the good guys) and leaves the door wide open for the fishy-smelling bacteria to move in and set up shop. The American College of Obstetricians and Gynecologists (ACOG) specifically recommends against douching for this exact reason. You are effectively killing the police force of your vaginal ecosystem and wondering why the crime rate went up.
✨ Don't miss: Is sex addiction real? Why the answer is more complicated than you think
Sweat and pH triggers
Sometimes the smell isn't coming from inside the vagina, but from the skin around it. The groin has a high concentration of apocrine sweat glands. These glands produce a thicker sweat that, when mixed with skin bacteria, can create a strong musky or slightly sour odor.
If you've been wearing synthetic leggings (looking at you, polyester yoga pants) all day, the lack of airflow creates a greenhouse effect. Heat plus moisture plus bacteria equals odor. This usually smells more like "sweaty gym bag" than "fish market," but the two can mix and create a confusing scent profile.
Diet also plays a minor role, though it's often exaggerated. Foods like asparagus, heavy garlic, or certain spices can subtly change the scent of your secretions, but they rarely produce a true "fishy" smell. That sharp, metallic or fishy scent is almost always bacterial.
When to actually see a doctor
If the smell persists for more than a couple of days, or if it's accompanied by pain, it’s time for a professional opinion.
A doctor will usually do a "whiff test." Yes, it’s exactly what it sounds like. They add potassium hydroxide to a sample of vaginal discharge; if a strong fishy odor is released, it’s a positive sign for BV. They might also look at the cells under a microscope to find "clue cells," which are vaginal cells covered in bacteria.
Treatment for BV is typically an antibiotic like Metronidazole or Clindamycin. You can get these as pills or as a vaginal gel. It is vital to finish the whole course, even if the smell vanishes after day two. If you stop early, the strongest bacteria survive and come back with a vengeance.
What about over-the-counter fixes?
You’ll see boric acid suppositories in every drugstore aisle now. They work by lowering the pH of the vagina to make it less hospitable to bad bacteria. For many women with recurrent BV, boric acid is a lifesaver. However, it’s a management tool, not always a cure for an active, heavy infection.
Warning: Boric acid is toxic if swallowed. Always keep it away from children and never take it orally.
Actionable steps to clear the air
If you're dealing with a fishy odor right now, here is your game plan.
- Ditch the soap. Use only warm water on the vulva (the outside). The inside needs nothing. If you must use soap, use a fragrance-free, very mild cleanser only on the hairy parts.
- Switch to cotton. Throw away the lace thongs for a few days. Cotton is breathable. Bacteria thrive in the damp, anaerobic environment created by synthetic fabrics.
- Probiotics might help. Look for strains specifically studied for vaginal health, like Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14. You can take these orally or find them in specific vaginal formulations.
- Hydrate. It sounds basic, but more water means more diluted urine and better overall mucosal health.
- Check for "the lost tampon." Do a quick manual check just to rule it out.
- Book an appointment. If you've tried the "wait and see" method for 48 hours and the scent is still there (or getting stronger), you likely need a prescription.
Vaginal health is a balancing act. It fluctuates with your period, your stress levels, and your diet. A slight change in scent throughout the month is normal. A fishy smell is a specific signal that the balance has tipped too far. Listen to it, treat it with respect, and stop over-cleaning. Your body knows how to handle the rest once you give it the right environment.