Strong-smelling urine is usually caused by concentrated waste products, particularly urea, building up when you haven’t had enough water. But dehydration is only one piece of the puzzle. Foods, vitamins, medications, and certain medical conditions can all change how your urine smells, sometimes dramatically. Most causes are harmless and temporary, but a few deserve attention.
Dehydration Is the Most Common Cause
Your kidneys filter waste from your blood and dissolve it in water to create urine. When you drink less fluid, there’s less water to dilute those waste products. The result is darker, more concentrated urine with a noticeably stronger ammonia-like odor. High levels of urea, the main nitrogen-containing waste product your body produces, are responsible for that sharp smell.
A simple way to gauge your hydration is urine color. Research published in the European Journal of Clinical Nutrition found that a urine color rating of 4 or higher on a standard scale (think apple juice or darker) reliably indicates concentrated urine. Pale straw or light yellow generally means you’re well hydrated. If your urine smells strong and looks dark, drinking more water throughout the day will typically resolve both within hours.
Foods That Change Urine Odor
Asparagus is the most notorious dietary trigger. Within a few hours of eating it, some people produce urine with a distinctly pungent sulfur smell. The odor comes from a cocktail of up to six sulfur-containing compounds, including methanethiol, dimethyl sulfide, and dimethyl disulfide. These are breakdown products of sulfur-rich molecules naturally present in the vegetable. Not everyone notices the smell: some people don’t produce these compounds, and others simply lack the ability to detect them.
Coffee is another common culprit. Your body breaks caffeine down into several metabolites (paraxanthine and theobromine are two major ones) that are excreted in urine and carry a distinct smell. Coffee also increases urine flow rate, which can make the odor more noticeable shortly after drinking it. Garlic, onions, and cruciferous vegetables like Brussels sprouts and cabbage contain their own sulfur compounds and can produce similar effects. Curry and other strong spices round out the list of frequent offenders.
B Vitamins and Supplements
If you take a multivitamin or B-complex supplement, you’ve probably noticed your urine turning bright greenish-yellow. That color change often comes with a stronger smell. Excess vitamin B6 (pyridoxine) gives urine a particularly strong odor, while too much vitamin B1 (thiamine) can produce a fishy smell. Your body can only use so much of these water-soluble vitamins at once, so it dumps the rest into your urine. The effect is harmless and disappears once the excess is cleared.
Urinary Tract Infections
A urinary tract infection (UTI) can make urine smell foul, cloudy, or unusually strong. Some bacteria that commonly cause UTIs, including Proteus mirabilis and Klebsiella pneumoniae, produce an enzyme called urease that breaks down urea into ammonia. This raises ammonia levels in the bladder directly, creating a sharp, unmistakable smell that’s different from the mild ammonia hint of concentrated urine.
A UTI rarely causes odor alone. You’ll typically also notice burning during urination, an urgent or frequent need to go, pelvic pressure, or urine that looks cloudy or pinkish. Fever, chills, or back pain suggest the infection may have reached the kidneys, which needs prompt treatment.
Diabetes and Metabolic Conditions
Uncontrolled diabetes can produce a sweet or fruity urine smell. When your body can’t use glucose properly, it burns fat for energy instead, producing chemicals called ketones. These ketones spill into your urine and carry a distinctive sweet odor. This is most common in type 1 diabetes but can also happen in type 2 during illness or when blood sugar runs very high for an extended period.
Rarer metabolic conditions can cause their own signature smells. Maple syrup urine disease, a genetic disorder affecting how the body processes certain amino acids, produces urine that smells like its namesake. Phenylketonuria (PKU) can give urine a musty quality. These conditions are almost always diagnosed in infancy through newborn screening.
Liver and Kidney Problems
Severe liver disease produces a characteristic sweet, musty odor in both urine and breath, known as fetor hepaticus. This happens when a failing liver can’t properly break down the amino acid methionine, leading to a buildup of sulfur compounds, specifically dimethyl disulfide and methyl mercaptan, that are excreted through the kidneys and lungs. This smell is a feature of advanced liver disease and would almost always appear alongside other obvious symptoms like jaundice, abdominal swelling, or confusion.
Kidney disease can also change urine odor by altering how efficiently waste products are filtered. As kidney function declines, the balance of waste compounds in urine shifts, sometimes creating an ammonia-heavy or otherwise unusual smell.
Other Common Triggers
Several everyday situations can temporarily change how your urine smells:
- Morning urine: You go six to eight hours without water overnight, so your first urine of the day is naturally more concentrated and stronger smelling.
- Exercise: Sweating reduces the water available for urine production, concentrating waste products the same way dehydration does.
- Pregnancy: Hormonal changes, prenatal vitamins (especially their B-vitamin content), and heightened sense of smell all contribute to noticing urine odor more during pregnancy.
- Antibiotics and other medications: Some antibiotics, particularly sulfonamides, and certain diabetes medications can alter urine smell as their metabolites are excreted.
How to Tell if It’s Serious
Most strong urine odor resolves with better hydration or fades once a food or supplement clears your system. A good test: drink an extra few glasses of water over several hours. If the smell fades and your urine lightens to pale yellow, dehydration or diet was likely the cause.
Odor that persists for several days despite good hydration is worth paying attention to, especially when paired with other changes. Burning or pain during urination, blood in your urine, fever, lower back pain, or urine that consistently smells sweet or fishy rather than just “strong” all point toward conditions that benefit from evaluation. A new, persistent sweet smell in particular warrants checking your blood sugar if you haven’t been screened for diabetes recently.