Strong-smelling urine is almost always concentrated urine. When your body doesn’t have enough water, your kidneys pull more of it back into your bloodstream and leave behind a higher percentage of waste products. That waste, especially a gas called ammonia, is what creates the pungent smell. In most cases, drinking more water will fix it within hours. But certain foods, vitamins, infections, and metabolic conditions can also change how your urine smells, even when you’re well hydrated.
Dehydration Is the Most Common Cause
Your kidneys constantly filter waste from your blood and mix it with water to produce urine. When you’re drinking enough fluids, urine is mostly water with a small amount of dissolved waste, and it has little to no odor. When you’re dehydrated, the ratio flips. The filtered waste takes a more prominent role, and ammonia concentration rises. That’s the sharp, almost chemical smell you notice.
You don’t need to be seriously dehydrated for this to happen. Sleeping through the night without drinking water is enough to produce dark, strong-smelling urine by morning. The same goes for a long workout, a hot day, or simply forgetting to drink throughout the afternoon. If your urine is pale yellow and nearly odorless after a glass or two of water, dehydration was likely the whole explanation.
Foods That Change Urine Smell
Asparagus is the most well-known offender. It contains a compound called asparagusic acid that your body breaks down into sulfur-containing byproducts during digestion. Those sulfur compounds pass into your urine and produce a distinctive, almost rotten smell that can appear within 15 to 30 minutes of eating. Somewhere between 20% and 50% of people experience this, though researchers aren’t sure whether the rest simply don’t produce the compounds or just can’t smell them.
Coffee is another common trigger. After your body processes coffee, compounds like guaiacol end up in your urine and give it a noticeable coffee-like odor. Garlic, onions, and cruciferous vegetables like Brussels sprouts and broccoli can also alter urine smell because they contain their own sulfur compounds. These food-related changes are harmless and temporary.
Vitamins and Supplements
B vitamins are a frequent culprit. Excess vitamin B6 can give urine a strong, sharp odor, while too much vitamin B1 can make it smell fishy. B vitamins also turn urine a bright greenish-yellow, which combined with a new smell can be alarming if you’re not expecting it. This happens because your body excretes whatever it doesn’t need, and water-soluble vitamins like the B complex pass straight through into urine when you take more than your body can use.
If you recently started a multivitamin, a B-complex supplement, or a prenatal vitamin and noticed a change, that’s very likely the cause.
Urinary Tract Infections
A urinary tract infection can make urine smell unusually strong, foul, or ammonia-like. Bacteria in the urinary tract break down urea (a normal waste product in urine) into ammonia, amplifying the smell beyond what even dehydration would cause. The odor is usually accompanied by other symptoms: burning or pain when you pee, a frequent urgent need to go, cloudy or discolored urine, or pelvic pressure. If you’re experiencing any of those alongside the smell, a UTI is a likely explanation and typically clears up quickly with treatment.
Diabetes and Ketones
A sweet or fruity urine smell is different from the usual ammonia sharpness, and it can signal a problem with blood sugar. When your body can’t use glucose for energy properly, it starts burning fat instead, producing waste products called ketones. One of those ketones, acetone, is responsible for the fruity odor. It shows up in your breath, sweat, and urine.
This is most concerning in the context of unmanaged diabetes, where it can indicate a dangerous condition called diabetic ketoacidosis. But mild ketone production also happens during very low-carb diets or extended fasting. If you’re noticing a sweet or fruity smell and haven’t intentionally changed your diet, especially if you’re also experiencing increased thirst, frequent urination, or fatigue, it’s worth getting your blood sugar checked.
A Fishy Smell May Be Genetic
A persistent fish-like odor in urine, sweat, and breath can point to a rare inherited condition called trimethylaminuria. People with this condition are missing or have a reduced version of a specific liver enzyme that normally breaks down a compound called trimethylamine. That compound is produced by gut bacteria when you digest eggs, fish, liver, and legumes like soybeans and peas. Without the enzyme working properly, trimethylamine builds up and gets released through body fluids, creating a strong fishy smell that doesn’t go away with hydration.
This condition is uncommon, but if you’ve always had unusually strong-smelling urine regardless of what you eat or drink, it’s worth mentioning to a doctor. Dietary adjustments that limit trimethylamine-producing foods can reduce the smell significantly.
Pregnancy and Smell Perception
If you’re pregnant and feel like your urine suddenly smells stronger, the change may be partly in your nose rather than in your urine. About two-thirds of pregnant women rate their sense of smell as higher than normal, and 85% identify at least one specific odor they’ve become more sensitive to. Common triggers include food smells, coffee, gasoline, and perfumes, but urine odor fits the same pattern.
Interestingly, when researchers actually measured pregnant women’s ability to detect faint odors in controlled tests, they found no significant difference compared to non-pregnant women. The change seems to be more about how odors are perceived and how unpleasant they feel, rather than a true increase in detection ability. Pregnancy also increases urination frequency, so dehydration can sneak up more easily, which may genuinely concentrate your urine on top of the heightened perception.
What Your Urine Color Tells You
Color and smell tend to track together because they’re driven by the same thing: concentration. Pale straw or light yellow urine with minimal odor means you’re well hydrated. Dark yellow or amber urine with a strong ammonia smell means your kidneys are conserving water. If your urine is dark and strong-smelling and stays that way even after you’ve been drinking water steadily for a day, something other than dehydration is likely at play.
Red or pink urine (when you haven’t eaten beets), consistently cloudy urine, or urine that smells foul rather than just strong are signs worth investigating. Paired with pain, fever, or changes in how often you need to urinate, these patterns suggest an infection or other condition that benefits from a proper evaluation.