Strong-smelling urine in adults is usually caused by something straightforward: not drinking enough water, eating certain foods, or taking supplements. Less commonly, it signals an infection or an underlying medical condition. The smell itself offers clues about what’s going on.
Dehydration Is the Most Common Cause
When you don’t drink enough water, your kidneys produce a more concentrated urine to conserve fluid. After several hours without water, such as overnight while you sleep, urine concentration can rise to roughly four times the concentration of your blood plasma. That concentrated urine packs more waste products, especially urea, into a smaller volume of liquid. The result is a darker yellow color and a sharper ammonia-like smell.
Urea is the main nitrogen-containing waste product your kidneys filter out. Your kidneys are actually remarkably efficient at concentrating urea, which reduces the total amount of water your body needs to excrete waste. But that efficiency means low water intake quickly produces noticeably pungent urine. Drinking more fluids throughout the day is the simplest fix. If your urine is pale yellow and the strong smell disappears, dehydration was likely the culprit.
Foods That Change Urine Odor
Asparagus is the most well-known offender. When you digest asparagus, a sulfur compound called mercaptan breaks down in your digestive system and gets excreted through urine. The smell typically appears within two hours of eating asparagus and peaks around that same window. Interestingly, about 60% of people can’t actually detect the odor due to a genetic variation. So if you’ve never noticed asparagus changing your urine smell, your nose may simply lack the receptors for it.
Garlic produces strong-smelling urine through a different pathway. Cutting or crushing garlic releases allicin, a sulfur compound that breaks down quickly after you eat it. The byproducts get excreted through both sweat and urine. Coffee, onions, and certain spices can also alter urine odor, though typically less dramatically than asparagus or garlic. These food-related smells are harmless and resolve once your body finishes processing the compounds.
Vitamins and Supplements
B vitamins are a frequent cause of strong or unusual urine odor, and they tend to turn urine a vivid bright yellow at the same time. Because B vitamins are water-soluble, your body excretes whatever it can’t absorb, and those excess compounds carry a distinct smell. Other water-soluble supplements can have the same effect. If you recently started a new multivitamin or prenatal supplement and noticed a change, that’s the likely explanation.
Urinary Tract Infections
Bacteria in the urinary tract produce chemical byproducts that give urine a foul, sometimes fishy smell. The most common culprit, E. coli, generates a compound called trimethylamine (TMA) as it breaks down substances in the bladder. TMA is the same chemical responsible for the characteristic smell of rotting fish. Another bacterium, Proteus mirabilis, metabolizes an amino acid called methionine in a completely different way, producing its own distinct set of odor-causing compounds.
A UTI smell is different from the ammonia smell of concentrated urine. It tends to be more foul and persistent regardless of how much water you drink. Other signs include a burning sensation during urination, cloudy urine, fever, chills, or back pain. If you notice these symptoms alongside the smell, an infection is the likely cause and needs treatment.
Diabetes and Ketones
When your body can’t use glucose for energy, either because of insufficient insulin or prolonged fasting, it starts burning fat instead. That process generates ketones, which spill into the urine and can produce a sweet or fruity smell. In people with diabetes, this can escalate into a dangerous condition called diabetic ketoacidosis (DKA), where ketone levels rise to harmful concentrations.
DKA doesn’t happen quietly. Along with the sweet urine smell, it typically causes nausea, vomiting, abdominal pain, shortness of breath, fruity-smelling breath, extreme fatigue, and confusion. This is a medical emergency. People following very low-carb or ketogenic diets may also notice a milder version of this fruity urine smell, which in that context is not dangerous but reflects the same metabolic process.
Liver and Kidney Disease
Severe liver disease produces a distinctive sweet and musty smell in both breath and urine, a phenomenon known as fetor hepaticus. This happens because the damaged liver can’t properly process an amino acid called methionine, leading to a buildup of sulfur-containing compounds that get excreted through urine, breath, and sweat.
Chronic kidney failure creates a different pattern. As the kidneys lose their ability to filter waste, urea accumulates and breaks down into ammonia, producing a strong ammonia smell. Fishy notes can also appear from the buildup of compounds called dimethylamine and trimethylamine. In both liver and kidney disease, the urine smell is just one symptom among many. Other signs like fatigue, swelling, skin changes, or appetite loss are usually present well before urine odor becomes noticeable.
Pregnancy
Many pregnant people notice their urine smells stronger, especially in the first trimester. The primary reason is often surprising: pregnancy heightens your sense of smell, a phenomenon called hyperosmia. Ammonia is always present in urine in small amounts, but a newly sensitive nose can pick up faint odors that were previously undetectable.
That said, real changes in urine odor do occur during pregnancy. Prenatal vitamins (particularly B vitamins) alter the smell. Dehydration from morning sickness concentrates the urine. And pregnant people face a higher risk of urinary tract infections, which produce their own distinct odor. Gestational diabetes can also cause sweet-smelling urine from excess glucose and ketones. If the smell is persistently strong and accompanied by other symptoms like pain or cloudiness, it’s worth investigating rather than assuming it’s just a pregnancy quirk.
When the Smell Points to Something Serious
Most strong urine odors resolve with simple changes: drinking more water, finishing the digestion of a pungent food, or adjusting your supplements. The smell becomes a concern when it persists for more than a day or two despite good hydration, or when it comes with other symptoms. Burning during urination, fever, chills, back pain, blood in the urine, or unexplained weight loss alongside a persistent odor change all warrant medical attention. A sweet or fruity smell in someone with diabetes needs prompt evaluation, since ketone buildup can become dangerous within hours.