Sulfur-smelling urine, often described as a “rotten egg” odor, is usually caused by something harmless like food or mild dehydration. In some cases, though, it can signal an infection or an underlying health condition worth investigating. The most common culprit by far is dietary: certain foods contain sulfur compounds that your body breaks down and excretes through urine.
Foods That Cause Sulfur-Smelling Urine
Asparagus is the most well-known offender. It contains a compound called asparagusic acid, which your body breaks down into several volatile sulfur byproducts during digestion. These byproducts are excreted in urine and can produce a noticeable sulfur smell within 15 to 30 minutes of eating asparagus. Not everyone can detect the odor, though. Genetic differences in smell receptors mean some people simply can’t perceive it.
Asparagus isn’t the only food that does this. Garlic, onions, and broccoli are all rich in sulfur compounds and can change the way your urine smells. Coffee is another common trigger. Foods high in B vitamins, including salmon, chicken, turkey, and beef, can also produce a noticeably funky urine odor. If sulfur-smelling urine shows up after a meal and disappears within a day, food is almost certainly the explanation.
Dehydration Concentrates the Odor
When you’re not drinking enough water, the compounds that give urine its smell become more concentrated. This makes any existing odor, including sulfur notes, much stronger and more noticeable. Dehydrated urine is also darker in color, ranging from deep yellow to amber. If your urine is both dark and strong-smelling, increasing your water intake for a day or two will typically resolve it. Think of dehydration as an amplifier: it doesn’t create new odors, but it makes existing ones impossible to ignore.
Urinary Tract Infections
A urinary tract infection is one of the most common medical causes of foul-smelling urine. Certain bacteria that infect the urinary tract produce sulfur-containing compounds as metabolic byproducts. Proteus mirabilis, a species frequently involved in UTIs, generates methanethiol (also called methyl mercaptan), dimethyl disulfide, hydrogen sulfide, and other sulfur chemicals when it breaks down amino acids. These are the same types of compounds responsible for the smell of rotten eggs.
A sulfur smell alone doesn’t confirm a UTI, but other symptoms make the picture clearer. Cloudy or slightly bloody urine, pain or burning during urination, a frequent urge to pee, fever, and mental confusion (particularly in older adults) all point toward infection. If the smell comes with any of these, it’s worth getting a urine test.
B Vitamins and Supplements
B vitamin supplements are a well-documented cause of unusual urine odor. They can make urine smell strong or unpleasant, and they also turn it a vivid bright yellow. This combination of intense color and odd smell often alarms people, but it’s simply the result of your body excreting the water-soluble vitamins it doesn’t need. Other water-soluble supplements can have a similar effect. If you recently started a new supplement and noticed the change, that’s likely the connection.
Liver Disease
Severe liver disease can produce a distinctive sweet, musty odor in both breath and urine. This condition, known as foetor hepaticus, is caused by the buildup of sulfur compounds, specifically dimethyl disulfide and methyl mercaptan. The liver normally processes the amino acid methionine, but when liver function is significantly impaired, excess methionine gets converted into these sulfur byproducts and excreted.
This is not a subtle symptom. It typically appears alongside other clear signs of liver trouble, such as jaundice (yellowing of the skin and eyes), abdominal swelling, fatigue, and dark urine. Isolated sulfur-smelling urine without these other signs is very unlikely to indicate liver disease.
Cystinuria and Genetic Conditions
Cystinuria is a rare inherited condition where the kidneys excrete too much of an amino acid called cystine into the urine. Excess cystine forms kidney stones, and these stones are associated with a sulfuric, rotten-egg smell. The condition tends to show up in childhood or early adulthood and often runs in families. People with cystinuria typically form kidney stones repeatedly, and diagnosis is made through chemical analysis of the stones, urine testing for cystine levels, or genetic testing from a blood or saliva sample.
If you’ve had recurring kidney stones, especially starting at a young age, and you notice sulfur-smelling urine, cystinuria is worth discussing with a doctor. For most people, though, this is a rare explanation.
When the Smell Matters
A one-time sulfur smell after eating asparagus or garlic is nothing to think twice about. The same goes for strong-smelling urine on a day you didn’t drink enough water. These are normal variations that resolve on their own.
The smell becomes worth paying attention to when it persists for several days without an obvious dietary explanation, or when it shows up alongside other symptoms: pain while urinating, cloudy or bloody urine, fever, flank pain, or changes in urine color that don’t match what you’ve been eating or drinking. Multiple symptoms together suggest something beyond diet or hydration, and a simple urine test can usually identify or rule out infection quickly.