A fishy smell from your genitals is most commonly caused by an overgrowth of certain bacteria that produce a chemical called trimethylamine. In people with vaginas, the overwhelmingly likely cause is bacterial vaginosis (BV), which affects roughly 1 in 3 women of reproductive age at some point. The smell can also come from a sexually transmitted infection, a hygiene-related issue (particularly in uncircumcised men), or, rarely, a metabolic condition. Most causes are treatable and nothing to be embarrassed about.
Bacterial Vaginosis: The Most Common Cause
A healthy vagina maintains a pH below 4.5, kept acidic by beneficial bacteria called lactobacilli. These bacteria produce lactic acid that keeps harmful microbes in check. When lactobacilli populations drop and other bacteria take over, the pH rises above 4.5, creating conditions where anaerobic bacteria thrive. These bacteria convert a compound called trimethylamine oxide into trimethylamine, the same chemical responsible for the smell of rotting fish.
BV is not a sexually transmitted infection, though sexual activity can trigger it. The telltale signs include a thin, white or gray discharge and a strong fishy odor that often gets worse after sex. Some people also experience burning during urination or itching around the vulva. Many people with BV have no symptoms at all other than the smell.
BV is diagnosed based on a combination of findings: the characteristic discharge, elevated vaginal pH, the fishy odor, and the presence of certain cells under a microscope. Your provider typically needs to confirm at least three of these four markers. Treatment is a course of antibiotics, either taken orally for about seven days or applied as a vaginal gel or cream for five to seven days. Symptoms usually clear within a week of starting treatment, though BV has a frustrating tendency to come back.
Trichomoniasis Can Smell Similar
Trichomoniasis is a sexually transmitted infection caused by a parasite, and it can produce a fishy smell that’s easy to confuse with BV. The discharge tends to be clear or white, sometimes with a greenish or yellowish tint, and may be frothy. Beyond the odor, trich often causes more noticeable irritation: redness, soreness, and itching of the genitals, along with discomfort during urination.
The key difference is that trich requires a different antibiotic and your sexual partners need treatment too, or you’ll pass it back and forth. If you’re noticing a fishy smell alongside significant genital irritation, trich is worth ruling out. It’s diagnosed with a simple swab test.
Causes in Men
A fishy or foul smell from the penis is most often related to smegma buildup, particularly in uncircumcised men. Smegma is a soft, whitish substance made of shed skin cells, sweat, and natural oils that collects under the foreskin. On its own it’s harmless, but when it isn’t cleaned away regularly, bacteria break it down and produce a noticeable odor.
If the smell comes with redness, pain, swelling of the head of the penis, or discharge from under the foreskin, you may have balanitis, an inflammation of the glans. Balanitis is most common in uncircumcised men and is usually caused by a combination of poor hygiene and bacterial or fungal overgrowth. Difficulty retracting the foreskin and pain during urination are other common signs. Treatment depends on the cause but often involves keeping the area clean and dry, along with a topical antibiotic or antifungal cream.
Why Douching Makes It Worse
If your instinct is to wash the smell away with a vaginal douche or scented product, that’s one of the worst things you can do. Douching disrupts the natural bacterial community inside the vagina and is strongly linked to developing BV. One study found that participants who douched within the previous six months had seven times the odds of having BV. Even douching once a month significantly increases your risk. Regular douching also raises the likelihood of pelvic inflammatory disease, a more serious infection of the uterus and fallopian tubes.
The vagina is self-cleaning. Warm water on the external area (the vulva) is all that’s needed. Scented soaps, wipes, and sprays can irritate the tissue and shift the pH in the same way douching does.
Foods and Supplements That Contribute
Certain foods can increase the amount of trimethylamine your body produces, and in some people this is enough to create a noticeable fishy odor in sweat, urine, and reproductive fluids. Foods high in choline and carnitine are the main culprits: eggs, liver, seafood, soy products, beans, broccoli, Brussels sprouts, cabbage, and cauliflower. Fish oil supplements, choline supplements, and carnitine supplements can also contribute.
For most people, normal amounts of these foods won’t cause a problem because a liver enzyme breaks trimethylamine down into an odorless form before it can accumulate. But if that enzyme isn’t working at full capacity, whether due to genetics, liver issues, or simply eating very large quantities of these foods, the unprocessed trimethylamine gets released through body fluids.
Trimethylaminuria: A Rare Metabolic Cause
If the fishy smell comes from your entire body, not just your genitals, and persists regardless of hygiene, you may have trimethylaminuria, sometimes called fish odor syndrome. This is a genetic condition where the liver enzyme responsible for breaking down trimethylamine (called FMO3) doesn’t work properly. The unprocessed chemical builds up and gets excreted in urine, breath, sweat, and reproductive fluids.
Primary trimethylaminuria is caused by inheriting two copies of a faulty gene, one from each parent. Secondary trimethylaminuria can develop if something overwhelms your FMO3 enzyme, like taking high-dose choline or carnitine supplements. The condition is rare, but if you’ve dealt with a persistent fishy body odor since childhood that no treatment seems to fix, it’s worth asking your doctor about a urine test that measures trimethylamine levels. Management focuses on avoiding trigger foods and sometimes taking low-dose supplements that help the enzyme work more efficiently.
What the Smell Is Telling You
A fishy odor that appears after sex and comes with thin, grayish discharge points strongly toward BV. A fishy smell with significant itching, redness, or frothy discharge suggests trichomoniasis. A foul smell localized under the foreskin, especially with redness or pain, points to smegma buildup or balanitis. A fishy odor that seems to come from your whole body, including your breath and sweat, raises the possibility of a dietary issue or trimethylaminuria.
Mild vaginal odor that shifts throughout your menstrual cycle is normal. What’s not normal is a strong, persistent fishy smell that wasn’t there before. BV accounts for the vast majority of these cases and clears up quickly with treatment, so there’s no reason to sit with the discomfort longer than you need to.