Few embarrassing situations are more universally understood than having smelly urine. Most people have experienced this after eating foods like asparagus or Brussel sprouts, causing some to worry about using a bathroom away from home when eating such foods over concerns of someone coming into the bathroom soon after they leave.  

But having odorous urine is something that happens to everyone – though it's certainly more commonly associated with eating some foods more than others. There are also times when an unpleasant odor may be associated with something other than dietary choices; and urine odor can even be a symptom of certain conditions that require medical attention.

Why does my pee smell?

Urine can smell for all kinds of reasons, "because urine consists of water and waste products your body doesn't need, which is why they're expelled," explains Olivia Baker, a registered dietitian and nutritionist at Mayo Clinic in Arizona. For example, when certain ingredients in medications like amoxicillin or supplements like vitamin B are processed out of the body, they often end up affecting urine odor.  

Dehydration can also change the way urine smells because when a person is dehydrated, their urine is more concentrated, which tends to make it smell like ammonia. 

Most commonly, though, "urine odor is affected by the foods we eat as there are many foods which have breakdown products that are excreted in the urine, which have characteristic odors," says Dr. Stephen Savage, a professor and interim chair of urology at the Medical University of South Carolina. 

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Which foods affects urine odor?

The food that probably has the most defining effect on urine odor, Savage notes, is asparagus. "Asparagus contains an acid that is broken down and then the kidneys excrete chemical compounds such as methanethiol and S-methyl thioester, which together create the characteristic odor," he explains. In fact, the "S" in S-methyl stands for sulfur, which is a notoriously pungent element. 

Another food that can affect urine odor is broccoli, which Savage says is metabolized in similar fashion to asparagus, including the excretion of methionine and its related sulfur smell. 

Other foods and beverages that Baker points to that are known to affect urine odor include coffee, black tea, cabbage, dried fruit, curry, alcohol, eggs, Brussel sprouts, garlic, cumin, onions and fish, "which can all affect the odor of your urine because the waste products of each food can contain chemical compounds that contribute to the overall smell." 

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Which medical conditions cause smelly urine? 

Beyond dietary choices, Savage says urinary tract infections can also cause odor - though most people experiencing one will have other symptoms and not just smelly urine. "There are also some unusual metabolic disorders that can cause abnormal urinary smells," he adds. 

Medical conditions such as chlamydia, bladder fistula, liver failure, trichomoniasis, gonorrhea and poorly controlled diabetes can also affect the smell of urine. "Diabetes can cause a sweet or fruity odor that can be a sign of something being amiss as well," says Savage, "so if the smell persists, it would be important to do a urinalysis." 

Baker similarly advises that, if you haven't consumed any food, supplement or medication known to affect urine odor, and your urine smells sweet or foul for longer than a couple of days, "it may be a sign of a medical condition that needs further evaluation."