Healthy urine has a mild, slightly earthy smell that most people would describe as faint or unremarkable. When you’re well-hydrated, the odor is barely noticeable. As urine becomes more concentrated from not drinking enough fluids, the smell gets stronger, sometimes taking on a sharper, ammonia-like quality. Both ends of that spectrum are normal.
What Gives Urine Its Typical Smell
Urine is mostly water, but it also contains urea, a waste product your body creates when it breaks down protein. Urea is the main source of urine’s baseline scent. At normal concentrations, it produces that mild, slightly acidic odor you’re used to. When you’re dehydrated, less water dilutes the urea and other waste products, so the smell intensifies. A strong ammonia smell after a night of sleep or a long stretch without water is one of the most common reasons people suddenly notice their urine’s odor, and it usually resolves once you drink more.
Foods That Change Urine Odor
Asparagus is the most well-known offender. It contains a compound called asparagusic acid, found only in asparagus, that breaks down into sulfur-containing byproducts during digestion. Those sulfur compounds pass into urine and create a distinctly pungent smell, often noticeable within 15 to 30 minutes of eating. Somewhere between 20% and 50% of people experience this, though researchers debate whether the rest simply don’t produce the compounds or just can’t detect the smell.
Coffee, garlic, onions, and certain spices can also leave a temporary mark on urine odor. These changes are harmless and disappear once the food clears your system.
Vitamins and Medications
B vitamins are a frequent cause of unexpectedly strong-smelling (and brightly colored) urine. B6 in particular can give urine a sharp or slightly metallic odor. If you’ve recently started a multivitamin or prenatal supplement and noticed a change, that’s likely the reason. Other water-soluble supplements can have a similar effect, since your body excretes whatever it doesn’t need through urine. Certain antibiotics, including sulfa drugs, can produce a sulfur-like smell as well.
Smells That Signal a Health Problem
Most day-to-day changes in urine odor are explained by hydration, food, or supplements. But a few distinct smells can point to something worth investigating.
Strong Ammonia or Foul Odor
A persistent, unusually foul or ammonia-heavy smell can indicate a urinary tract infection. Many of the bacteria responsible for UTIs break down urea into ammonia, which intensifies the smell well beyond what dehydration alone would cause. This is usually accompanied by other signs like burning during urination, cloudy urine, or an urge to go more frequently.
Sweet or Fruity Smell
Urine that smells sweet or fruity may signal that your body is producing ketones, acids created when you burn fat for energy instead of glucose. This happens during very low-carb dieting, prolonged fasting, or, more seriously, in uncontrolled diabetes. In diabetic ketoacidosis, ketone levels become dangerously high and spill into urine. If you notice a fruity smell and haven’t been restricting carbohydrates intentionally, it’s worth checking your blood sugar.
Musty or Earthy Smell
A musty, slightly sweet, or decaying odor can be associated with liver problems. When the liver can’t properly process certain waste compounds, substances like dimethyl sulfide build up in the blood and eventually come out in urine, sweat, and breath. This distinctive smell, sometimes described as musty or like rotten eggs, tends to appear alongside other signs of liver trouble such as jaundice, fatigue, or abdominal swelling.
Maple Syrup or Burnt Sugar Smell
A rare inherited condition called maple syrup urine disease prevents the body from breaking down three specific amino acids: leucine, isoleucine, and valine. These build up to toxic levels and give urine, sweat, and earwax a smell resembling maple syrup or burnt sugar. This condition is typically identified in newborns through routine screening.
Urine Odor During Pregnancy
Many pregnant people notice that their urine smells different, sometimes stronger or more metallic. Several factors contribute at once. Rising levels of hCG and progesterone change how the kidneys filter waste and fluid, which can alter urine concentration and odor. Blood volume increases significantly during pregnancy, pushing more fluid through the kidneys. Prenatal vitamins, especially their B-vitamin content, add another layer. And heightened sense of smell during pregnancy, a well-documented phenomenon driven by hormonal shifts, means you may simply be detecting odors you would have ignored before.
When Urine Odor Is Worth Paying Attention To
A one-time change in smell after eating asparagus or starting a new vitamin is nothing to think twice about. The patterns worth noting are persistent changes that last more than a day or two without an obvious dietary explanation, or odors accompanied by other symptoms like pain, fever, unusual color, or increased frequency. A sweet or fruity smell in someone who isn’t intentionally fasting or following a ketogenic diet deserves prompt attention, as it can indicate a blood sugar emergency. A foul smell paired with cloudy or dark urine points toward possible infection.
Your baseline is your best reference point. If you’re well-hydrated and not taking any supplements, your urine should have little to no odor. Anything that represents a clear, lasting departure from that baseline is your body communicating something worth investigating.