Sweat smells like ammonia when your body breaks down protein for energy and the resulting waste products end up in your perspiration. The sharper and more noticeable the smell, the more ammonia your body is producing or the less effectively it’s being cleared. For most people, the cause is dietary or exercise-related, but in some cases it signals a problem with the kidneys or liver.
How Ammonia Ends Up in Your Sweat
Your body prefers to burn carbohydrates for fuel. When carbs aren’t available, it turns to protein instead. Breaking down protein produces nitrogen as a byproduct, and your liver converts that nitrogen into ammonia, then into urea, which your kidneys filter out through urine. That’s the normal pathway.
When ammonia is produced faster than your liver and kidneys can process it, blood levels of ammonia rise. Research published in the European Journal of Applied Physiology confirmed that plasma ammonia is the principal source of ammonia in sweat. In other words, the ammonia you smell on your skin didn’t form on the surface. It traveled through your bloodstream and was excreted by your sweat glands. The higher the ammonia concentration in your blood, the stronger the smell in your sweat.
Exercise Is the Most Common Trigger
If you’ve noticed the ammonia smell during or after a hard workout, you’re not imagining it. During prolonged or intense exercise, your muscles burn through their glycogen (stored carbohydrate) reserves. Once those stores run low, your body increasingly breaks down amino acids from protein to keep producing energy. That process generates more ammonia than usual, and the excess spills into your sweat.
A study on prolonged nonexhausting exercise found that people who started their workout with reduced carbohydrate stores had significantly higher ammonia concentrations in both plasma and sweat compared to those with normal stores. The takeaway is straightforward: the less glycogen you have available, the more protein your body burns, and the more ammonia you produce. Long endurance sessions, fasted workouts, and training without adequate carb intake all increase the likelihood of that ammonia smell showing up.
Diet Plays a Major Role
What you eat in the hours and days before a workout, or just in general, directly affects how much ammonia your body produces.
High-protein diets are the most obvious contributor. When you eat more protein than your body needs for muscle repair and other functions, the excess gets broken down for energy. That means more nitrogen waste, more ammonia production, and a stronger smell in your sweat. If you’re eating a lot of protein without enough carbohydrates to match, the effect intensifies because your body is forced to rely even more heavily on amino acids as fuel.
Low-carb and ketogenic diets compound the problem from both directions. First, they limit the carbohydrate your muscles can use for energy, pushing your body toward protein and fat metabolism. Second, ketosis itself produces acetone, which is excreted through breath and sweat. Ammonia combined with acetone can create a particularly sharp, unpleasant odor on your skin, breath, and in your urine. Getting the ratio of protein to fat wrong on a keto diet, specifically eating too much protein, makes the ammonia component worse.
Dehydration Concentrates the Smell
Dehydration doesn’t cause your body to produce more ammonia, but it makes the ammonia you do produce more noticeable. When you’re well-hydrated, your sweat is more dilute, and ammonia is spread across a larger volume of fluid. When you’re dehydrated, the same amount of ammonia is concentrated in less sweat, making the smell stronger and more detectable. Dehydration also reduces your kidney output, which means less ammonia is being cleared through urine and more ends up in your bloodstream, where it can be excreted through the skin.
When It Points to a Health Problem
For most people, ammonia-smelling sweat is a sign they need to adjust their diet or hydration. But persistent ammonia odor that doesn’t respond to dietary changes can indicate that your body’s ammonia-clearing systems aren’t working properly.
Kidney Disease
Your kidneys are responsible for filtering urea and other nitrogen waste products out of your blood. When kidney function declines, ammonia that would normally leave through urine builds up in the bloodstream instead. That elevated blood ammonia then gets excreted through sweat and breath. People with kidney disease often notice an ammonia or urine-like smell on their skin or breath that persists regardless of diet or exercise habits. Northwestern Medicine identifies an ammonia smell as one of the body odor changes that can signal kidney problems.
Liver Disease
Your liver is the organ that converts toxic ammonia into urea in the first place. When it’s damaged, as in cirrhosis or liver failure, this conversion process breaks down. Ammonia accumulates in the blood, and you may notice its smell in your sweat. Advanced liver disease can also produce a distinct odor called fetor hepaticus, sometimes described as smelling like rotten eggs and garlic, caused by a mix of compounds including ammonia, acetone, and other volatile substances. According to the Cleveland Clinic, fetor hepaticus typically appears in the late stages of chronic liver disease and indicates the liver is no longer filtering blood effectively. If toxins accumulate at high enough levels to smell on your breath, they may be affecting your brain and nervous system as well.
How to Reduce Ammonia Smell
If the ammonia smell is tied to exercise or diet, you have several practical levers to pull.
- Eat carbohydrates before and during long workouts. Keeping your glycogen stores topped off reduces the amount of protein your body breaks down for energy. Even a moderate carb-containing snack before exercise can make a difference. For workouts lasting over an hour, consuming carbs during the session helps too.
- Rebalance your protein intake. If you’re eating significantly more protein than you need, especially on a low-carb diet, the excess is being burned for fuel and converted to ammonia. Bringing protein closer to the amount you actually use for recovery (rather than treating it as your primary energy source) reduces ammonia production.
- Stay hydrated. Drinking enough water dilutes ammonia in your sweat and helps your kidneys clear it more efficiently through urine. This won’t eliminate the underlying production, but it noticeably reduces the intensity of the smell.
- Don’t train fasted if the smell bothers you. Fasted workouts deplete glycogen faster and push your body toward protein metabolism sooner. Having some fuel on board delays that shift.
If you’ve tried these adjustments and the ammonia smell persists, or if you notice it at rest without any obvious dietary or exercise explanation, it’s worth having your kidney and liver function checked. A basic blood panel can measure markers of both and rule out the less common but more serious causes.