Unusual urine odor is almost always caused by something harmless: what you ate, how much water you drank, or a supplement you’re taking. In most cases, the smell resolves on its own within a day or two. But certain persistent or strong odors can signal an infection, a metabolic issue, or a more serious underlying condition worth paying attention to.
What Normal Urine Smells Like
Fresh urine has a mild, slightly acidic smell that most people barely notice. That faint scent comes from a mix of waste products your kidneys filter out of your blood, including small amounts of ammonia. The smell only becomes noticeable when something changes the concentration or chemical makeup of your urine.
Dehydration Is the Most Common Cause
If your urine is dark yellow and smells strong, you’re likely not drinking enough water. When your body is low on fluids, your kidneys conserve water by producing less urine. That means the same waste products get packed into a smaller volume, and the ammonia that’s always present becomes far more concentrated. The higher the concentration, the stronger the smell.
This is especially common first thing in the morning, after exercise, or on hot days. Drinking more water dilutes your urine, lightens its color, and usually eliminates the odor entirely.
Foods That Change Urine Odor
Asparagus is the most famous culprit. Your body breaks down asparagusic acid, a compound found in asparagus, into sulfur-containing molecules like methanethiol (the same chemical that gives natural gas its rotten-egg warning smell) and dimethyl sulfide. These volatile compounds pass through your kidneys and into your urine, sometimes within 15 to 30 minutes of eating. Not everyone produces these compounds, and not everyone can smell them, which is why some people swear asparagus doesn’t affect their urine.
Other foods that commonly change urine smell include garlic, onions, Brussels sprouts, curry, and coffee. The effect is temporary and disappears once your body finishes processing the food.
Vitamins and Supplements
B vitamins are well known for giving urine a strong, sometimes sulfurous smell along with a bright neon-yellow color. This happens because B vitamins are water-soluble. Your body absorbs what it needs and flushes the rest through your kidneys. The yellow color comes from riboflavin (B2), and the odor is a byproduct of excess B6 and other B-complex vitamins being excreted.
Prenatal vitamins, which contain high doses of B vitamins and iron, are a frequent source of this change. Other water-soluble supplements can also alter urine odor. If the smell started around the same time you began a new supplement, that’s likely the connection.
Urinary Tract Infections
A strong, foul, or fishy urine smell that doesn’t go away with hydration may point to a urinary tract infection. Certain bacteria that colonize the urinary tract produce enzymes that break down urea (a normal waste product in urine) into ammonia and carbon dioxide. One of the most common offenders, Proteus mirabilis, is particularly efficient at this. It generates so much ammonia that it actually changes the pH of your urine, making it highly alkaline.
Smell alone isn’t enough to diagnose a UTI, but if you also have a burning sensation when you urinate, a frequent or urgent need to go, cloudy or pink-tinged urine, lower abdominal pressure, fever, chills, or back pain, those are signs that warrant a visit to your doctor. UTIs are easily treated but can spread to the kidneys if ignored.
Diabetes and Sweet-Smelling Urine
A sweet or fruity urine odor can be a sign of uncontrolled diabetes. When your body can’t use glucose properly, it starts burning fat for energy instead, producing waste products called ketones. These ketones spill into your urine and give it a distinctive sweet or acetone-like smell, similar to nail polish remover. This is more common in type 1 diabetes but can also occur in type 2 diabetes during periods of very high blood sugar.
If you notice a persistent sweet smell and you haven’t been diagnosed with diabetes, it’s worth getting your blood sugar checked, especially if you’re also experiencing increased thirst, frequent urination, or unexplained weight loss.
Pregnancy and Heightened Smell
Many pregnant people notice their urine smells different, particularly in the first trimester. Part of this is real and part of it is perceptual. Hormonal shifts in early pregnancy trigger hyperosmia, a dramatically heightened sense of smell. That faint ammonia scent that was always in your urine suddenly becomes impossible to ignore.
At the same time, pregnancy does change urine chemistry. Morning sickness and nausea can lead to dehydration, concentrating the urine. Prenatal vitamins add their own odor. And pregnant people are more susceptible to UTIs due to changes in the urinary tract, so a new or worsening smell during pregnancy is worth mentioning to your provider.
Liver Problems and Musty Odor
A persistent musty or garlicky smell in your urine, breath, or sweat can indicate liver disease. When the liver can’t properly filter toxins from the blood, volatile compounds like dimethyl sulfide and methyl mercaptan build up and get excreted through urine, sweat, and breath. Dimethyl sulfide produces a pungent, garlicky odor, while methyl mercaptan smells more like rotten eggs or overcooked cabbage. Ammonia, acetone, and other compounds may contribute as well.
This characteristic smell, known clinically as fetor hepaticus, tends to appear in advanced liver disease. It wouldn’t be the first or only sign. You’d likely also notice fatigue, jaundice (yellowing skin or eyes), abdominal swelling, or dark urine for other reasons. But if the smell is persistent and unfamiliar, and especially if paired with any of those symptoms, it’s worth investigating.
Rare Genetic Conditions
A persistent fishy smell that doesn’t respond to diet changes or hydration could point to trimethylaminuria, sometimes called fish odor syndrome. This condition involves a problem with the FMO3 enzyme, which normally processes trimethylamine, a compound produced during digestion of certain foods like eggs, fish, and legumes. When the enzyme doesn’t work properly, trimethylamine accumulates and gets released in urine, sweat, and breath, producing a strong fishy odor.
Trimethylaminuria can be inherited or acquired secondary to other conditions. It’s diagnosed through a urine test that measures trimethylamine levels, sometimes followed by genetic testing. It’s rare, but if you’ve had an unexplained fishy body odor for as long as you can remember, it’s a possibility worth raising with your doctor.
What Different Smells Can Tell You
- Strong ammonia: Usually dehydration or concentrated urine. Can also signal a UTI.
- Sulfurous or rotten eggs: Asparagus, garlic, onions, or other sulfur-rich foods.
- Sweet or fruity: Possible uncontrolled diabetes or ketosis from very low-carb diets.
- Fishy: UTI, bacterial vaginosis (which can be confused with urine odor), or rarely trimethylaminuria.
- Musty or garlicky: Potential liver issues if persistent.
- Chemical or medicinal: Certain medications or supplements being excreted.
A one-time odd smell after a meal or a dehydrated morning is nothing to worry about. The signals that matter are persistence (lasting more than a couple of days despite good hydration), accompanying symptoms like pain, fever, or blood in your urine, or a smell so strong and unusual that it clearly departs from your normal baseline.