Is Smelly Urine Anything to Worry About?

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Why does urine smell?

Most healthy adult humans produce around six and a half cups of urine daily. Human urine contains water as well as other products that are excreted by the body through the kidneys. Since 95% of urine is water, it is uncommon for fresh urine to have a bad smell. The sense of smell does vary among individuals, and some people may notice a mild smell to their urine that is not typically offensive in nature. The pungent odor of stale urine (think of a busy and dirty public restroom) is likely due to the presence of volatile organic compounds, or VOC’s, which are present in urine. More than 200 VOC’s have been identified in human urine. As urine ages, it undergoes evaporation of water which leads to a change in the concentration of VOC’s in the urine. The concentrated VOC’s that are present in older urine, including dimethyl sulfone, trimethylamine (TMA), and acetic acid, are often smelly compounds that are likely contributors to the characteristic smell of old urine.

VOC’s are also present in breath, sweat, and other body fluids, and vary based on our age, diet, health status, and other factors. Many of these VOC’s contribute to our individual body odor. Some studies have identified a connection between the presence of some VOC’s and different diseases such as leukemia, liver disease, and kidney failure. In humans, VOC’s present in urine have been explored as potential targets for search and rescue dogs assisting in the rescue of entrapped victims of building collapses and other disasters.

Is smelly urine anything to worry about?

Food, drink, and our body’s metabolism can affect the composition of our urine as well as its odor. One of the most common causes of an abnormal urine odor is asparagus. After eating asparagus, many people report having a sulfur-like odor to their urine. The cause of this is unknown but may be related to the presence of VOC’s, including dimethyl sulfoxide, methanethiol, or carbon disulfide, which are present in the urine of people who eat asparagus. Interestingly, some individuals are unable to smell the pungent urine odor associated with asparagus consumption. Urinary odors can be associated with certain medical conditions, so if odor persists or occurs on a regular basis it is important to see a doctor for further evaluation. Urinary tract infections involve the presence of mucus, bacteria, and white blood cells in urine. Many of the bacterial species that cause urinary tract infections can also break down urea, a natural waste product that is commonly excreted in urine. These bacteria cause urea to break down into ammonia, which imparts a strong, pungent odor to affected patients’ urine. Another cause of an abnormal urine smell is diabetes, which may be associated with sweet-smelling urine due to the presence of excess glucose or sugar in the urine. Some genetic conditions are also associated with an abnormal urine smell. In maple syrup urine disease, affected patients’ urine typically smells sweet. Patients with kidney disease or dehydration may have concentrated urine that contains an abnormally high level of waste products and smells like ammonia.

Why does my urine smell like fish?

Patients affected by trimethylaminuria will often have fishy-smelling urine. Trimethylaminuria is a genetic disorder in which affected individuals have an enzymatic deficiency that makes them unable to metabolize TMA. Because they cannot metabolize TMA, affected individuals have a buildup of TMA in their bodies. This excess TMA is then excreted in sweat, urine, and other body fluids. While many individuals with trimethylaminuria are diagnosed as infants or children, the disease is sometimes not detected until adulthood, and it may also occur intermittently. Emotional distress, menstruation, use of oral contraceptives, and consumption of foods or dietary supplements rich in choline are all factors that may worsen the signs and symptoms of trimethylaminuria, including the presence of fishy-smelling urine. Because of the significant odor associated with the disease, many patients with trimethylaminuria suffer from psychological distress, including loneliness, depression, and avoidance of social situations.

Choline is an essential nutrient that is present in cell membranes. Consumption of choline, which is present in multiple vitamins and supplements (including vitamin B6 and prenatal vitamins), can cause a fishy urine odor in individuals who have trimethylaminuria. Meat, fish, dairy, and egg products are also good dietary sources of choline and may worsen urinary odor in patients with trimethylaminuria. Use of oral contraceptive pills may also result in a fishy urine odor in affected individuals. The ingestion of other foods and dietary supplements that contain odiferous VOC’s, including garlic, may also affect urine odor. 

If you develop an abnormal urine odor or other undesirable symptoms after taking medications or dietary supplements, talk to your doctor or contact Poison Control. Get an immediate personalized recommendation online or call 1-800-222-1222. Both options are free, confidential, and available 24 hours a day.