Strong-smelling urine usually comes down to something simple: what you ate, how much water you drank, or a supplement you’re taking. In most cases, the smell is temporary and harmless. But persistent or unusual odors, especially paired with other symptoms like pain or cloudiness, can signal infections, blood sugar problems, or rarer metabolic conditions worth investigating.
Dehydration Is the Most Common Cause
When you don’t drink enough water, your kidneys produce less urine, and the waste products in it become more concentrated. That concentration intensifies the natural ammonia smell of urine, sometimes to the point where it’s sharp and unpleasant. The fix is straightforward: drink more fluids. If your urine is pale yellow and the smell is mild, you’re well hydrated. Dark amber urine with a strong odor is your body telling you it needs more water.
Foods That Change Urine Odor
Asparagus is the most well-known offender. Your body breaks down a compound called asparagusic acid into sulfur-containing molecules, primarily methanethiol, which give urine a distinct smell similar to cooked cabbage. This happens quickly, sometimes within 15 to 30 minutes of eating asparagus. Interestingly, not everyone can detect the smell. A genetic variation near an olfactory receptor gene called OR2M7 determines whether you can perceive the odor. Some people produce it but genuinely cannot smell it.
Other foods that commonly alter urine smell include garlic, onions, Brussels sprouts, curry, and coffee. These effects are harmless and disappear once the food clears your system, typically within a day or two.
Vitamins, Supplements, and Medications
B vitamins are frequent culprits. High doses of vitamin B6 can give urine a strong, pungent odor, while excess vitamin B1 can make it smell fishy. If you’ve recently started a multivitamin or B-complex supplement and noticed a change, that’s likely the connection.
Certain medications alter urine odor too. Sulfonamide antibiotics, commonly prescribed for urinary tract and other bacterial infections, can give urine a noticeable stench. Some diabetes and rheumatoid arthritis medications have the same side effect. The smell typically lasts as long as you’re taking the medication and resolves after you stop.
Urinary Tract Infections
A sudden ammonia-like or foul smell in your urine, especially if it’s cloudy or slightly bloody, often points to a urinary tract infection. Bacteria in the urinary tract break down urea, a normal waste product in urine, into ammonia and carbon dioxide. One species, Proteus mirabilis, is particularly efficient at this. Its urease enzyme rapidly hydrolyzes urea, raising the pH of urine and creating a strongly alkaline environment. That alkaline shift is also what allows mineral crystals to form, sometimes leading to kidney stones made of struvite and apatite.
Beyond the smell, UTI symptoms include a burning sensation when you pee, a frequent or urgent need to urinate, and sometimes pelvic pressure. Fever and mental confusion, particularly in older adults, are signs the infection may have spread and needs prompt attention. If the smell appears alongside any of these symptoms, it’s worth getting a urinalysis.
Diabetes and Ketoacidosis
Sweet or fruity-smelling urine can be a warning sign of high blood sugar. When your body can’t use glucose properly, either because of uncontrolled diabetes or insufficient insulin, it starts burning fat for fuel instead. That process produces ketones, including acetone, which gives both breath and urine a distinctive sweet or fruity scent.
This is especially concerning when ketone levels climb high enough to cause diabetic ketoacidosis, a potentially life-threatening condition. If you notice a persistent sweet smell and you have diabetes, or if it’s accompanied by excessive thirst, frequent urination, nausea, or fatigue, don’t wait on it.
Liver Disease
Severe liver dysfunction produces a characteristic sweet, musty smell in both urine and breath, a clinical sign known as foetor hepaticus. The odor comes from the buildup of dimethyl disulfide and methyl mercaptan, sulfur compounds that accumulate when the liver can’t properly process the amino acid methionine. This is not a subtle change. It tends to appear alongside other signs of advanced liver disease like jaundice, abdominal swelling, and confusion.
Rare Genetic and Metabolic Conditions
Trimethylaminuria (Fish Odor Syndrome)
Some people produce urine, sweat, and breath that smell strongly of fish. The cause is an inherited deficiency in a liver enzyme called FMO3, which normally converts a compound called trimethylamine (TMA) into an odorless form. Without enough functional enzyme, TMA builds up and gets excreted through urine, sweat, and breath. Under normal conditions, gut bacteria produce TMA from dietary sources like choline, found in eggs, liver, and certain fish. In people with this enzyme deficiency, the TMA passes into the bloodstream and can’t be neutralized. The smell can range from mild to severe and often worsens after eating TMA-rich foods.
Maple Syrup Urine Disease
In newborns, sweet-smelling urine that resembles maple syrup is a red flag for a rare but serious genetic disorder called maple syrup urine disease. This condition involves a defective enzyme complex (BCKAD) that normally breaks down three essential amino acids: leucine, isoleucine, and valine. When these amino acids and their byproducts accumulate, a compound called sotolone, an isoleucine metabolite, gives the urine and even earwax its signature maple syrup scent. This condition is life-threatening without treatment and is typically caught through newborn screening.
When the Smell Matters
A one-time change in urine odor after eating asparagus or taking a new supplement is nothing to worry about. The real signal is persistence. Foul-smelling urine that lasts more than a couple of days, or that shows up alongside pain, cloudiness, blood, fever, or unusual thirst, is worth a medical visit. Sweet-smelling urine in particular should not be dismissed, in adults or in children, since it can indicate blood sugar problems or metabolic disorders that benefit from early detection.