Your urine always contains ammonia. It’s a normal byproduct of protein metabolism, and in most cases, a strong ammonia smell simply means your urine is more concentrated than usual. The most common reason is not drinking enough water, but diet, infections, pregnancy, and a few medical conditions can also intensify the smell.
How Ammonia Ends Up in Your Urine
When your body breaks down protein from food, it produces nitrogen waste. Your liver converts most of that waste into a compound called urea, which dissolves easily in water and travels to your kidneys. From there, it leaves your body in urine. Some of that urea gets broken down further into ammonia, both inside the body and after urine leaves it. Bacteria in your gut also break down about 3.6 grams of nitrogen per day from urea, recycling ammonia back to the liver.
The ammonia is always present. What changes is how noticeable it is. When your urine is diluted with plenty of water, the ammonia concentration stays low and you barely smell anything. When the urine is concentrated, that same ammonia is packed into less fluid, and the smell becomes sharp and obvious.
Dehydration Is the Most Common Cause
If your urine is dark yellow and smells strongly of ammonia, dehydration is the most likely explanation. Your kidneys need water to dilute waste products. When you’re not drinking enough, they produce smaller volumes of more concentrated urine, and the ammonia smell intensifies proportionally. This is especially common first thing in the morning, after sleeping for hours without drinking anything.
The fix is straightforward: drink more water. Most adults need roughly 8 to 12 cups per day, though needs increase with exercise, heat, and illness. If your urine is pale yellow and the smell fades, dehydration was probably the whole story.
Diet and Supplements
A high-protein diet increases the amount of nitrogen your body needs to process. More protein means more urea, which means more ammonia in your urine. If you’ve recently increased your intake of meat, eggs, dairy, or protein shakes, that alone can explain a stronger smell.
Specific foods can also change how your urine smells. Asparagus is the most well-known example, but garlic and onions can shift the odor too. B vitamins, particularly B6, and prenatal vitamins are common supplement culprits. The smell from foods and vitamins is temporary and harmless, usually clearing within a day of stopping the trigger.
Urinary Tract Infections
Certain bacteria that cause urinary tract infections produce an enzyme called urease, which breaks urea down into ammonia directly inside your urinary tract. This can make your urine smell strongly of ammonia even when you’re well-hydrated. The bacterium most associated with this process is Proteus mirabilis, which breaks down urea at rates 6 to 25 times faster than related species. That aggressive ammonia production is also why Proteus infections are frequently linked to kidney stone formation.
UTI-related ammonia smell usually comes with other symptoms: burning during urination, a frequent urgent need to go, cloudy urine, or pelvic discomfort. If you notice ammonia odor alongside any of these, an infection is a strong possibility. UTIs are treatable with antibiotics, and the smell resolves once the infection clears.
Struvite Kidney Stones
When urease-producing bacteria linger in the urinary tract, they can cause a specific type of kidney stone called a struvite stone. These stones form from a mix of magnesium, ammonium, and phosphate. The bacteria make urine less acidic, creating conditions where these minerals crystallize. Cloudy or bad-smelling urine is a common symptom, along with back or flank pain and sometimes fever.
Struvite stones are different from the more common calcium-based stones because they’re driven by infection rather than diet. Treatment typically involves removing the stone and clearing the underlying bacterial infection. In some cases, a medication that blocks bacteria from producing ammonia is prescribed to prevent stones from returning.
Pregnancy
Pregnant people commonly notice changes in how their urine smells. Several factors converge at once: the body’s fluid needs increase significantly, food cravings shift the diet, and prenatal vitamins (especially those with B6) alter urine chemistry. Dehydration is particularly common in early pregnancy when nausea makes it harder to keep fluids down.
The American College of Obstetricians and Gynecologists recommends pregnant people drink 8 to 12 cups of water daily, which works out to 64 to 96 ounces. Holding urine for too long during pregnancy can also increase UTI risk and cause the urine to smell more like ammonia, so urinating when you feel the urge matters more than usual. If the smell persists despite good hydration, it could point to a UTI or gestational diabetes, both of which are routinely screened for during prenatal care.
Hormonal Changes After Menopause
After menopause, declining estrogen levels change the chemistry of the vaginal environment. The vaginal walls thin, natural moisture decreases, and the pH shifts from acidic to more alkaline. This shift increases susceptibility to both vaginal infections and UTIs, either of which can produce ammonia-like odors that seem to come from the urine.
The smell may actually be vaginal rather than urinary, since the two are close enough to be easily confused. If you’re postmenopausal and noticing a new ammonia odor, a UTI or vaginal infection is worth investigating. Douching is not a helpful response here. It strips beneficial bacteria and further disrupts pH balance, often making the problem worse.
Less Common Medical Causes
Liver disease can change the smell of both breath and urine, though the odor it produces is typically described as sweet and musty rather than sharp like ammonia. This smell comes from sulfur-containing compounds that build up when the liver can’t process amino acids properly. It’s a sign of severe liver dysfunction, not early-stage disease, and almost always comes with other noticeable symptoms like jaundice, fatigue, or abdominal swelling.
Uncontrolled diabetes can also alter urine odor, though the characteristic smell is more fruity or sweet (from ketones) than ammonia-like. Kidney disease that impairs the organs’ ability to filter waste can increase urea and ammonia levels in the body, sometimes making both urine and sweat smell different.
When the Smell Is Worth Investigating
A one-time ammonia smell after a hard workout, a night of poor hydration, or a high-protein meal is not concerning. Drink more water and see if it resolves. The situations that warrant a closer look are:
- Persistent smell despite good hydration: if you’re drinking plenty of water and the ammonia odor lasts more than a few days, something beyond concentration is likely driving it.
- Pain or burning during urination: strongly suggests a UTI or other urinary tract issue.
- Cloudy or discolored urine: cloudiness combined with ammonia odor is a classic UTI pattern.
- Fever or back pain: may indicate a kidney infection, which is a UTI that has spread upward and needs prompt treatment.
- New onset during pregnancy: worth mentioning at your next prenatal visit, especially if accompanied by other urinary symptoms.
In most cases, ammonia-smelling urine is your body telling you to drink a glass of water. But when the smell sticks around or brings friends like pain, cloudiness, or fever, it’s a signal worth paying attention to.