A persistent fishy smell coming from your body, breath, or urine usually points to a buildup of specific nitrogen-containing compounds, most commonly trimethylamine. The source can range from something as routine as a vaginal infection or a dietary supplement to something less common like a genetic condition or organ disease. Where the smell is coming from and how long it lasts narrows down the likely cause considerably.
Vaginal Odor and Bacterial Vaginosis
The most common reason women notice a fishy smell is bacterial vaginosis (BV), a condition where the normal balance of vaginal bacteria shifts. Healthy vaginal flora is dominated by lactobacillus bacteria that keep the environment acidic, typically at a pH between 4.0 and 4.5. When those bacteria are depleted, other organisms move in and start producing compounds called biogenic amines, specifically putrescine, cadaverine, and trimethylamine. These are the direct chemical source of the fishy odor.
Beyond the smell, BV typically causes a creamy gray discharge and a vaginal pH above 4.5. The odor often becomes more noticeable after sex or during a period because semen and blood are alkaline, which makes those amines more volatile. BV is not a sexually transmitted infection, though sexual activity can trigger it. It’s treated with a short course of antibiotics, and the smell resolves once the bacterial balance is restored.
Trimethylaminuria: A Genetic Cause
Some people produce a fishy body odor that has nothing to do with infection. Trimethylaminuria, sometimes called fish odor syndrome, is a metabolic condition where the body can’t properly break down trimethylamine (TMA), a compound generated in the gut when bacteria digest certain nutrients. Normally, a liver enzyme converts TMA into an odorless form. In people with trimethylaminuria, that enzyme is deficient or absent, so TMA accumulates and gets released through sweat, breath, and urine.
The condition is diagnosed with a urine test that measures the ratio of TMA to its odorless byproduct. In unaffected people, more than 80% of TMA is converted to the odorless form. In people with trimethylaminuria, that ratio drops well below 80%, sometimes to 40% or lower. The smell can range from barely noticeable to severe, and it often fluctuates with diet, hormonal changes, and stress.
Management focuses on reducing the raw material that gut bacteria turn into TMA. That means limiting foods high in choline, carnitine, and lecithin: things like eggs, organ meats, saltwater fish, and certain legumes. Using body washes with a slightly acidic pH (around 5.5 to 6.5) can also help neutralize TMA on the skin surface. Some people respond to riboflavin (vitamin B2) supplements, which support whatever residual enzyme activity they have.
Supplements That Cause Fishy Odor
You don’t need a genetic condition to smell like fish after taking certain supplements. Choline supplements, particularly choline bitartrate, can cause a fishy body odor at high doses. This happens through the same pathway: gut bacteria convert the choline into trimethylamine, and if you’re taking enough of it, your liver’s conversion capacity gets overwhelmed. L-carnitine supplements can do the same thing. Reducing the dose or switching to a different form of the supplement usually eliminates the problem.
Urinary Tract Infections
A fishy smell in your urine can signal a urinary tract infection, particularly one caused by certain bacterial species. Proteus bacteria, a common culprit in UTIs, produce a characteristic fishy odor as they grow. The smell is often accompanied by cloudy or dark urine, a burning sensation during urination, and increased urgency. UTIs caused by Proteus species tend to also raise urine pH, which can increase the risk of kidney stones if left untreated.
Kidney Disease and Uremic Breath
When the kidneys lose their ability to filter waste, compounds that would normally leave through urine start building up in the blood and get exhaled through the lungs instead. This produces a distinctive breath odor that has been described as fishy, ammoniacal, or like stale urine. The specific chemicals responsible are ammonia, trimethylamine, and dimethylamine, all of which have a rotten-fish quality.
Fishy breath from kidney dysfunction doesn’t appear in isolation. It typically accompanies other signs of advanced kidney disease: fatigue, swelling in the legs, nausea, changes in urination patterns, and itchy skin. If you’re noticing fishy breath alongside any of these, it warrants prompt medical evaluation.
Liver Disease
Advanced liver disease produces its own characteristic breath odor, called fetor hepaticus. This is often described as sweet and musty rather than purely fishy, but some people perceive it as a fishy or sulfurous smell. The primary chemical behind it is dimethyl sulfide, which builds up when the liver can’t properly process sulfur-containing amino acids. Like uremic breath, this is a late-stage finding that comes with other obvious symptoms of liver failure, including jaundice, abdominal swelling, and confusion.
Phantom Smells From Nerve Damage
Sometimes the fishy smell isn’t coming from your body at all. Phantosmia is the perception of an odor when no odor source is present, and parosmia is when real smells get distorted into something unpleasant. Both can make you perceive a fishy or rotten smell that nobody else notices.
These conditions most commonly develop after a viral infection that damages the olfactory neurons in the nose. The leading theory is that as those neurons regenerate, they “miswire,” connecting to the wrong targets in the brain. Odor signals that should register as neutral or pleasant get routed through pathways associated with foul smells instead. Brain imaging studies have confirmed that people with parosmia show abnormal activation patterns in their smell-processing regions when exposed to ordinary odors.
Post-viral smell distortion became much more widely recognized after COVID-19, but it can follow any upper respiratory virus. For most people, the distorted smells gradually improve over months as the olfactory neurons continue regenerating. Smell training, which involves deliberately sniffing a set of strong, distinct scents twice daily, appears to support this recovery process by helping the brain relearn correct odor associations.
Sweat That Smells Fishy
Fishy-smelling sweat that isn’t explained by trimethylaminuria could be a form of bromhidrosis, or chronic body odor. The sweat glands in your armpits, groin, and around the nipples (apocrine glands) produce an oily, odorless fluid. When bacteria on the skin surface break that fluid down, they release ammonia and short-chain fatty acids that can smell sour, pungent, or occasionally fishy. The specific bacteria involved, particularly Corynebacterium species, determine the exact character of the odor.
This type of body odor responds well to antibacterial soaps, topical antibiotics, or antiperspirants that reduce both moisture and bacterial populations. Wearing breathable fabrics and changing clothes after sweating also helps.