The Causes of Foul-Smelling Urine

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Urine can take on all sorts of smells, which is logical because it's created from waste in our bodies. From an ammonia smell to a fishy odor, Bilal Kaaki, MD, UnityPoint Health, identifies what causes foul-smelling urine.

What is Urine?

Dr. Kaaki says urine is made of mostly water, but it also has salt (sodium, potassium and chloride), uric acid and urea. Uric acid is a natural waste product from food digestion and urea is a waste product made of ammonia and carbon dioxide—all substances the body tries to get rid of through urine.

“The kidneys filter out the excess water, excess salt and other materials the body wants to get rid of. That’s how urine is formed, Dr. Kaaki says. “After going through the kidneys, urine goes through ureters and then gets collected into the bladder. It sits in the bladder until we feel an urge to empty the bladder.” 

Foul-Smelling Urine: Dehydration

Dr. Kaaki says the number one reason for bad-smelling urine is dehydration. 

“You always have a certain amount of ammonia in your urine. When you have more water, the ammonia is diluted, and it smells less intense. Whereas with dehydration, the concentration of ammonia is going to be higher and the smell would be stronger,” Dr. Kaaki says.

To avoid dehydration, watch the amount of water you drink on a daily basis. Dr. Kaaki says a lot of factors impact your ability to stay hydrated, including size, weight, medical conditions, kidney function, daily activity level and heat and humidity of the day. 

“However, 30 to 40 ounces of fluid in a day is a general rule. That includes any kind of fluid you drink, not just water. That means milk, tea, water, coffee, soda, juice and even water in the foods we eat. The more fruits and vegetable you have in your diet, the higher the water contents,” Dr. Kaaki says.

Foul-Smelling Urine: Food

Asparagus is the number one food linked to bad-smelling urine. If you’ve heard some people say their pee doesn’t smell after eating asparagus, Dr. Kaaki gives this response.

“It’s an urban legend. Everyone’s urine smells when eating asparagus. The person that is saying it does not smell is pulling our leg,” Dr. Kaaki says.

Asparagus contains an acid (asparagusic acid) that causes a sulfur-like smell. When you eat the vegetable, you ingest the acid, which goes to your blood stream, kidneys and makes its way to urine in your bladder. 

Besides asparagus, other top offenders in the food category include:

  • Fish. In general, your urine contains the chemical compounds from food you’ve eaten.
  • Onion. This vegetable has a certain compound, which carries the unpleasant onion-like smell through the body.
  • Garlic. It is in the same family as onions, therefore acting in the same manner.

Foul-Smelling Urine: Vitamins & Medication

Eating fish isn’t the only reason your urine might have a fishy smell. Dr. Kaaki says vitamin B and vitamin D can cause a similar smell. Keep in mind these vitamins are in most multivitamins. 

Dr. Kaaki says medication from the sulfa drug group can also cause your urine to smell bad.

  • Sulfonamide antibiotics. An example is Bactrim, which is commonly used to treat UTIs.
  • Diabetes medications. These sulfa drugs are sold under the names Diabeta, Glynase PresTabs.
  • Rheumatoid arthritis medications. This sulfa drug is sold under the name of Azulfidine.

Foul-Smelling Urine: Medical Conditions

There are several medical conditions causing foul-smelling urine. Dr. Kaaki explains the most common diagnosis with this side effect. 

  • Yeast infection. Dr. Kaaki says it’s the vaginal discharge smell that changes, not actually the urine. But he notes when you use the bathroom your urine mixes with vaginal discharge and it’s hard to distinguish where the smell is coming from. He describes the smell as sweet, which comes from the yeast.
  • Sexually transmitted infections (STIs). Like yeast infections, vaginal discharge in the case of STIs causes a mild smell, not urine itself. STIs can also cause a mild-smelling urine for men, too. In that case, the infection is often in the urethra in the penis. The urine passes through the urethra before exiting the body.
  • Kidney stones. Kidney stones could change the smell of urine due to ammonia. In addition to ammonia this condition often puts more salts in the urine, which can change the smell to be a bit more unusual, but not necessarily foul-smelling. Dr. Kaaki says kidney stones are diagnosed with pain and a change in the urine color more often than the smell.
  • Uncontrolled Diabetes. While diabetes medication can cause foul-smelling urine, so can uncontrolled diabetes. Uncontrolled diabetes causes sugar in the urine, making it smell sweeter. In healthy individuals, there isn’t usually sugar in urine.
  • Urinary Tract Infections (UTIs). Bacterial overgrowth from a UTI causes a foul smell in urine. Dr. Kaaki compares it to a skin abscess. When the abscess infection is opened, there’s a foul smell from the bacterial overgrowth. The foul-smelling urine from a UTI is caused in the same manner.

Foul-Smelling Urine: Pregnancy

Dr. Kaaki says there is really no change in the smell of urine for a pregnant woman, but there is a change in her nose. The change in hormones in expectant moms can result in a heightened sense of smell. It’s called hyperosmia.

“That’s why early in their pregnancy some women can’t tolerate certain smells, whether it’s perfume or certain foods. The increased sense of smell might cause a pregnant woman to notice the smell of urine more, even though it hasn’t really changed,” Dr. Kaaki says.

In addition to the increased sense of smell, Dr. Kaaki says a few other things might cause a pregnant woman’s urine to change odors. 

“Some women, early in pregnancy, might have more sickness or vomiting or they are having diarrhea, so they become dehydrated. Prenatal vitamins also have vitamin B and D, which we discussed can cause foul-smelling urine. Pregnant women are also more prone to UTIs,” Dr. Kaaki says.

When to Visit the Doctor for Foul-Smelling Urine

Since the primary cause of foul-smelling urine is dehydration, Dr. Kaaki suggests increasing your water intake for 24 hours. If the smell persists, or if you notice any additional symptoms of pain, urgency or change in urine color, contact your clinic. Often, your provider can make it easy for you by simply putting in an order for a urine sample at the lab. Then, you can skip the clinic visit and jump right to finding answers to why you might be feeling bad.