Sweat that smells like pee almost always comes down to one chemical: ammonia. Both urine and sweat contain ammonia and its precursor, urea, so when ammonia levels rise in your sweat, the two smells converge. Healthy sweat contains about 20 to 25 millimoles per liter of urea, but diet, exercise intensity, and certain medical conditions can push that number significantly higher.
The Ammonia Connection
Your body constantly produces ammonia as a byproduct of breaking down proteins and other nitrogen-containing compounds. Amino acids from food go through a process called deamination, which strips off nitrogen and releases free ammonia. Normally, your liver converts most of that ammonia into urea, which your kidneys then filter out through urine.
But your kidneys aren’t the only exit route. Sweat glands also excrete urea and small amounts of ammonia directly. Bacteria living on your skin then break down that urea into additional ammonia using enzymes called ureases. So even if your sweat starts out relatively mild, the microbes on your skin can amplify that urine-like smell within minutes, especially in warm, enclosed areas like your armpits or groin.
Low-Carb Diets and Protein-Heavy Eating
Diet is the most common reason otherwise healthy people notice this smell. Your body prefers to burn carbohydrates for energy because they convert to glucose quickly. When carbs are scarce, whether from a ketogenic diet, intermittent fasting, or simply skipping meals before a workout, your body turns to protein as a backup fuel source. That protein breakdown floods your system with amino acids, which get converted into ammonia at a rate your liver and kidneys can’t always keep up with. The overflow exits through your sweat.
You don’t need to be on a strict keto diet for this to happen. Eating a very high-protein meal before exercise, or consistently under-eating carbohydrates relative to your activity level, can produce the same effect. Adding more complex carbohydrates before workouts is often enough to reduce or eliminate the smell.
Intense Exercise Burns More Than Calories
Hard training increases ammonia production regardless of diet. During prolonged or high-intensity exercise, your muscles burn through their glycogen stores (the body’s carbohydrate reserves) and begin breaking down amino acids, including those from muscle tissue, for extra energy. The nitrogen released from those amino acids gets converted to ammonia, which spills into your bloodstream and eventually into your sweat.
This is why the smell tends to be worse during long endurance sessions or intense interval training, and less noticeable during a casual walk. The harder your body works and the less glycogen it has available, the more protein it burns and the more ammonia-scented your sweat becomes. Staying well-fueled with carbohydrates before and during extended exercise is the most straightforward fix.
Dehydration Concentrates the Smell
When you’re dehydrated, your body produces less sweat overall, but the sweat it does produce is more concentrated. That means the same amount of urea and ammonia is dissolved in less fluid, making the smell stronger and more urine-like. Dehydration also reduces your kidneys’ ability to clear ammonia efficiently through urine, so more of it gets diverted to sweat. Drinking enough water throughout the day dilutes both your urine and your sweat, which can noticeably reduce the odor.
Skin Bacteria Make It Worse
The smell isn’t entirely about what’s in your sweat. Bacteria on your skin play a major role. Species like Micrococcaceae, diphtheroids, and Propionibacteria break down sweat components into volatile molecules, including ammonia and short-chain fatty acids. Other bacteria with strong urease activity, such as certain strains of E. coli and Proteus, are particularly efficient at converting urea into ammonia. Areas of the body with more bacteria and less airflow, like the groin, feet, and underarms, tend to produce the strongest urine-like smell for this reason.
Showering promptly after exercise, wearing breathable fabrics, and using antibacterial soap on odor-prone areas can reduce the bacterial contribution to the smell.
Kidney and Liver Problems
When the smell persists regardless of diet or hydration, it could signal that your kidneys or liver aren’t processing waste effectively. Normally, your liver converts ammonia to urea and your kidneys excrete it. If either organ is compromised, ammonia and urea accumulate in your blood and eventually seep out through your skin and breath.
In kidney disease, urea concentrations in sweat can climb to 50 millimoles per liter, roughly double the normal range. This condition, called uremia, produces a characteristic ammonia or bleach-like odor from the skin and breath known as “uremic fetor.” Liver cirrhosis causes a similar problem from the other direction: the liver loses its ability to convert ammonia to urea in the first place. Studies on cirrhosis patients found breath ammonia levels nearly three times higher than in healthy controls, and those levels climbed even further when ammonia was accumulating in the blood.
These are serious conditions with other noticeable symptoms. If the urine-like smell comes alongside persistent fatigue, swelling in your legs or face, changes in how often you urinate, unexplained nausea, or yellowing skin, those are signs worth getting checked promptly.
Other Medical Causes
A few other conditions can raise ammonia in sweat. Uncontrolled diabetes sometimes produces a fruity or acetone-like body odor, but in some cases it overlaps with ammonia production due to altered metabolism. Hyperhidrosis, a condition involving excessive sweating even at rest or during sleep, can make any underlying odor more noticeable simply by increasing the volume of sweat your skin bacteria have to work with. Certain medications that affect liver or kidney function may also contribute.
Practical Ways to Reduce the Smell
- Eat enough carbohydrates before exercise so your body doesn’t rely heavily on protein for fuel.
- Stay hydrated to dilute urea and ammonia in both urine and sweat.
- Shower soon after sweating to wash away urea before skin bacteria convert it to ammonia.
- Wear moisture-wicking fabrics that reduce the warm, damp environment bacteria thrive in.
- Moderate protein intake if you’re consuming significantly more than your body needs, especially on low-carb diets.
For most people, sweat that smells like pee is a temporary and diet-related issue. Adjusting your carbohydrate and fluid intake before physical activity typically resolves it within a day or two. A persistent ammonia smell that doesn’t respond to these changes, especially with other unexplained symptoms, points toward something worth investigating with bloodwork to check kidney and liver function.