Why Do I Smell Like Ammonia When I Sweat?

Ammonia-scented sweat usually means your body is burning more protein than usual for fuel and excreting the nitrogen byproducts through your skin. Sweat naturally contains ammonia at concentrations far higher than what circulates in your blood, so even a modest uptick in nitrogen metabolism can push the smell past your nose’s detection threshold. The causes range from mundane dietary choices to the intensity of your workout, though in rare cases persistent ammonia odor can flag a medical issue worth investigating.

How Ammonia Gets Into Sweat in the First Place

Your sweat glands do not simply pump out a copy of your blood plasma. The fluid in your eccrine sweat ducts is slightly acidic, and ammonia, a small uncharged molecule, drifts from plasma into that acidic environment by passive diffusion. Once inside the duct, the acidic pH traps the ammonia as ammonium ion, which cannot easily diffuse back out. This trapping mechanism concentrates ammonia in sweat to roughly 20 to 50 times its level in plasma.¹ Research on healthy volunteers, patients with liver cirrhosis, and patients with kidney disease confirmed that plasma ammonia is the principal source of ammonia in sweat: when blood ammonia went up, sweat ammonia followed.²

So the question “why does my sweat smell like ammonia?” really comes down to two things: what is raising ammonia in your blood, and how efficiently your sweat glands are concentrating it. Both are influenced by what you eat, how hard you exercise, and how hydrated you are.

The Role of Protein, Carbs, and What Your Muscles Are Burning

Your body prefers to run on carbohydrates and fat. Protein is a fuel of last resort because breaking it down for energy produces nitrogen waste, and that nitrogen has to go somewhere. When it goes through the liver, it becomes urea and leaves via your kidneys. But some of that nitrogen takes a shortcut and circulates as ammonia, which your sweat glands readily absorb and concentrate.

Several things tilt your muscles toward burning more amino acids. The most common one for otherwise healthy people is eating a high-protein, low-carbohydrate diet. A study comparing a low-carbohydrate diet to a normal diet during moderate cycling found that plasma ammonia was higher on the low-carb diet at both 30 and 60 minutes of exercise. Sweat ammonia concentration and total ammonia lost through sweat were also higher.³ The researchers attributed this to reduced starting carbohydrate stores, which forced the body to lean harder on amino acids for fuel. If you have noticed the ammonia smell after switching to a keto or very-low-carb plan, this is likely the mechanism at work.

Branched-chain amino acids, the ones heavily marketed in fitness supplements, are a particularly large contributor to exercise ammonia. Research on cyclists showed that BCAAs are an important source of ammonia during moderate-intensity exercise, and that increasing BCAA availability through supplementation significantly increased ammonia production.⁴ So if you are loading up on BCAA powder before a workout, you may actually be making the smell worse.

Why Long or Intense Workouts Make It Worse

Even on a balanced diet, the ammonia smell tends to appear during hard or prolonged exercise. Two distinct processes explain why.

During short, high-intensity efforts, your muscles produce ammonia mainly from the breakdown of a molecule involved in energy transfer. This process ramps up sharply as exercise intensity approaches your maximum.⁵ That is why sprinters and people doing heavy lifting sometimes notice a whiff near the end of a tough set, even though the workout is brief.

During longer exercise at moderate intensity, a second pathway takes over. As muscle glycogen runs low, your muscles increasingly rely on amino acid deamination for energy. In a study of prolonged one-leg cycling, ammonia release gradually climbed and plateaued after about an hour at roughly 80 micromoles per minute. The total ammonia produced far exceeded what could be accounted for by nucleotide breakdown alone, confirming that amino acid deamination was the major source.⁶ Interestingly, the same study found that starting with lower glycogen stores in one leg did not significantly change total ammonia output at moderate intensity, suggesting that amino acid breakdown proceeds at a fairly steady clip during sustained work regardless of initial fuel status.

At higher intensities, though, glycogen depletion does change the picture. When glycogen runs out during intense exercise, lactate production drops but ammonia keeps climbing, creating a divergence that researchers have proposed as a marker for glycogen depletion in exercise testing.⁵ Practically speaking, this means the ammonia smell is most likely to hit you in the second half of a long workout, during back-to-back sessions, or toward the end of a race when your carbohydrate stores are low.

Where on Your Body the Smell Hits Hardest

You have two types of sweat glands, and they do not contribute equally to the problem. Eccrine glands, the small ones distributed over most of your skin, produce the watery sweat you notice during exercise and heat. Apocrine glands, concentrated in your armpits, groin, and around the nipples, secrete a thicker fluid that bacteria love to feed on.

A study comparing the composition of eccrine and apocrine sweat found that urea excretion from apocrine glands was substantially higher than from eccrine glands under the same conditions, and that both glands secreted more urea during active running than during passive heating.⁷ Urea itself is not ammonia, but skin bacteria readily convert urea into ammonia, which is part of the reason armpits and the groin smell worse than, say, your forearms. The combination of apocrine secretions rich in nitrogen-containing compounds and a warm, moist environment that encourages bacterial breakdown makes those areas the epicenter of ammonia odor.

This is also why the smell sometimes seems worse after you stop exercising and your sweat begins to sit on your skin. While you are actively sweating heavily, the sheer volume of fluid dilutes ammonia. Once sweat rate drops and bacteria have time to work on the residue, the concentration climbs and the smell intensifies.

Hydration Matters More Than You Might Think

Because ammonia concentration in sweat is inversely related to sweating rate, dehydration makes the problem worse in two ways.¹ First, when you are dehydrated, you produce less total sweat, which means ammonia gets less diluted. Second, reduced fluid intake limits your kidneys’ ability to clear urea and ammonia through urine, so more of that nitrogen waste circulates in your blood and gets picked up by your sweat glands. People who report an ammonia smell while barely breaking a sweat during a moderate walk in hot weather often find that simply drinking more water before and during activity is enough to make it fade.

Age and Sex Differences

Not everyone sweats out the same amount of ammonia. Children tend to have higher sweat ammonia concentrations than adults, likely because they sweat less overall. In a study measuring sweat composition during exercise in the heat, girls and boys both had significantly higher sweat ammonia than women and men during an initial exercise bout. Girls averaged about 4.2 millimolar and boys about 4.6 millimolar, compared to roughly 2.7 for women and 3.0 for men.⁸ The difference persisted into a second exercise bout among girls and women but not among boys and men, hinting that sex-based differences in sweat gland maturation and sweating rate play a role.

Older adults often notice the ammonia smell more, too, though for different reasons. Aging kidneys are slightly less efficient at clearing nitrogen waste, and older adults tend to have lower muscle glycogen stores, which means they may shift to amino acid oxidation sooner during exercise. If you are over 60 and find the smell new or worsening, it is worth mentioning to your doctor, but it does not automatically mean something is wrong.

When the Smell Could Signal a Medical Problem

For most people, ammonia-smelling sweat is a benign side effect of diet and exercise choices. But a few conditions can drive blood ammonia high enough to make the odor persistent and hard to ignore, even at rest.

Liver disease: The liver is where ammonia gets converted to urea for excretion by the kidneys. When the liver is damaged or cirrhotic, this conversion slows down and blood ammonia rises. Since plasma ammonia is the principal source of sweat ammonia, liver problems can produce a noticeable smell even without exertion.²
Kidney disease: Kidneys clear urea. When they cannot keep up, urea accumulates in the blood and can appear on the skin as a gritty residue sometimes called “uremic frost.” The smell associated with advanced kidney failure is often described as ammonia-like, though urea itself is odorless until bacteria break it down.
Urea cycle disorders: These are rare inherited conditions in which the enzymes responsible for converting ammonia to urea are partially or fully absent. Patients with urea cycle disorders commonly report body odor as a symptom. In clinical trials of a treatment for these disorders, about 69 percent of patients reported treatment-associated symptoms including body odor before intervention, and the proportion dropped significantly with treatment.⁹
Uncontrolled diabetes: In diabetic ketoacidosis, the body’s inability to use glucose forces heavy reliance on fat and protein for fuel. The resulting nitrogen waste can produce ammonia-like odor, though the more characteristic smell of ketoacidosis is fruity or acetone-like. If your sweat smells like ammonia and you also feel excessively thirsty, urinate frequently, or notice unexplained weight loss, blood sugar testing is warranted.

A useful rule of thumb: if the ammonia smell appears only during or shortly after hard exercise and goes away with a shower, diet and exercise intensity are the overwhelmingly likely explanation. If the smell persists at rest, cannot be washed off, or is accompanied by other symptoms like fatigue, confusion, nausea, or swelling, see your doctor and ask for a blood ammonia level and basic metabolic panel.

Practical Steps to Reduce the Smell

Since the underlying cause for most exercisers is nitrogen metabolism, the most effective fixes target what you eat and how you fuel your workouts.

Add carbohydrates around exercise: Eating some carbs before or during a workout helps keep glycogen available so your muscles rely less on amino acids. This directly reduces ammonia production. The difference between a low-carb and normal diet on sweat ammonia is large enough to be measured in lab studies.³
Moderate protein intake: If you are eating well above your body’s protein needs, the excess gets burned for energy and the nitrogen is excreted. Most people do not need more than about 1.6 grams of protein per kilogram of body weight per day, even during heavy training.
Reconsider BCAA supplements: BCAAs are a direct contributor to exercise ammonia production.⁴ If you are already eating adequate protein, supplementing with BCAAs adds little performance benefit but may worsen the smell.
Stay hydrated: More fluid means more dilute sweat and better kidney clearance. Drink enough to produce pale yellow urine before your workout.
Shower promptly: Bacteria on the skin convert urea and other nitrogen compounds into ammonia. Rinsing off quickly after exercise reduces the time bacteria have to amplify the smell.
Wear breathable fabrics: Moisture-wicking clothing pulls sweat away from the skin and lets it evaporate, reducing the warm, damp environment that bacteria thrive in.

The Emerging Science of Sweat Monitoring

Ammonia is one of several analytes that wearable sweat sensors can now detect in real time. Researchers are developing patches and wristbands that track ammonia, lactate, glucose, and electrolytes during exercise, with the goal of giving athletes and patients feedback about their metabolic state without a blood draw. The technology is still in early stages and faces practical hurdles: sweat composition changes depending on flow rate, body site, and how long the sensor has been on the skin. No single analyte in sweat provides a reliable standalone picture of health, so the devices need to measure multiple markers simultaneously to be useful.

For athletes, a real-time ammonia reading could eventually serve as a signal that glycogen stores are running low, since ammonia production ramps up as carbohydrate availability drops.⁵ That information could help runners and cyclists decide when to take in more fuel during a long event, potentially improving performance while also cutting down on the post-race ammonia cloud. For patients with liver disease or urea cycle disorders, non-invasive ammonia monitoring through sweat could reduce the need for frequent blood tests, though clinical validation is still years away.