The Causes of Foul-Smelling Urine
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, Christine Davis, DO, UnityPoint Health, identifies what causes foul-smelling urine.
What is Urine?
Dr. Davis 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. 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. Davis says. “After going through the kidneys, urine goes through ureters and then collects in the bladder, until we feel an urge to urinate.”
Foul-Smelling Urine: Dehydration
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 higher, and the smell is stronger,” Dr. Davis says.
What Causes Dehydration?
To avoid dehydration, watch the amount of water you drink on a daily basis. Dr. Davis says a lot of factors impact your ability to stay hydrated, such as:
- Daily activity level
- Heat and humidity of the day
- Kidney function
- Medical conditions
- Size
- Weight
“Between 60-80 ounces of fluid a day is recommended for most adults. 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. Please note that some health conditions require fluid restriction, so always follow your doctor's recommendations,” Dr. Davis says.
Foul-Smelling Urine: Food
Asparagus is the number one food linked to bad-smelling urine. It 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 makes your urine smell because it contains trimethylamine oxide, which is broken down by gut bacteria into a compound with a strong fishy odor that’s excreted in urine and sweat.
- Garlic contains compounds that give it a strong flavor. Some of these compounds are released in your urine after your body breaks them down, giving it a distinctive odor.
- Onions, like garlic, contain sulfur compounds that give them their strong flavor. After you eat onions, your body breaks down these compounds — some of which are released in your urine, which can make it smelly.
Foul-Smelling Urine: Vitamins & Medication
Eating fish isn’t the only reason your urine might have a fishy smell. Dr. Davis says vitamin B and vitamin D cause a similar aroma. Keep in mind these vitamins are in most multivitamins. Certain medications, like those from the sulfa drug group, also cause a change in the smell of your urine.
Here are some examples:
- Sulfonamide antibiotics
- Diabetes medications, like Diabeta, Glynase PresTabs
- Rheumatoid arthritis medications, such as Sulfasalazine
Foul-Smelling Urine: Medical Conditions
Several underlying health issues cause foul-smelling urine. Dr. Davis explains the most common diagnoses with this side effect.
- Yeast infection: When you use the bathroom, your urine mixes with vaginal discharge, and it’s hard to distinguish where the smell is coming from. The smell might be sweet, which comes from the yeast.
- Sexually transmitted infections (STIs): Like yeast infections, vaginal discharge from STIs causes a mild smell, not the urine itself. STIs create a mild-smelling urine for men, too, and the infection is often in the urethra in the penis. Urine passes through the urethra before exiting the body.
- Kidney stones: They could change the smell of urine due to ammonia. Kidney stones put more salt in urine, too, which can change the smell. However, a change in urine smell alone isn't a sure sign of a kidney stone.
- Uncontrolled diabetes: Diabetes medication and uncontrolled diabetes can cause foul-smelling urine. When blood sugar is high, sugar spills into your urine, which can make it smell slightly sweet.
- Urinary tract infections (UTIs): A UTI can cause urine to smell foul due to bacterial growth, but a change in urine smell alone doesn't always mean you have an infection.
Foul-Smelling Urine: Pregnancy
Dr. Davis says there's really no change in urine smell when a woman's pregnant, but there is a change in her nose.
“That’s why early in their pregnancy some women can’t tolerate certain smells, whether it’s perfume or 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. Davis says.
In addition to the increased sense of smell, a few other things might cause a pregnant woman’s urine to change odors.
“Early in pregnancy, some women have morning sickness, vomiting or diarrhea, so they become dehydrated. Prenatal vitamins also have vitamin B and D, which we discussed can cause foul-smelling urine,” Dr. Davis says.
When to Visit the Doctor for Foul-Smelling Urine
Since the primary cause of foul-smelling urine is dehydration, Dr. Davis suggests increasing your water intake for 24 hours. If the smell persists, or you notice additional symptoms of pain, urgency or change in urine color, contact your doctor.