You finish a long run and realize your shirt doesn’t just smell like sweat. It smells like a cleaning product. Sharp, pungent, distinctly chemical. That’s ammonia, and if you’ve experienced it, you know it’s a different category from regular post-workout sweat smell.
The good news: ammonia-smelling sweat is usually explainable by something you’re doing with your diet or training, not something going wrong inside you. Here’s what’s happening and how to address it.
The Biochemistry: Where the Ammonia Comes From
Ammonia in sweat comes from the metabolism of amino acids. To understand why, a quick detour into how your body uses fuel:
Your body’s preferred energy sources are carbohydrates (converted to glucose and glycogen) and fat. Protein is used for building and repairing tissue, not as a primary fuel source. But under certain conditions, your body begins to metabolize amino acids (the building blocks of protein) for energy through a process called gluconeogenesis.
When amino acids are broken down for energy, nitrogen is stripped off. This nitrogen is converted to ammonia (NH3) by the liver, which then converts most of it to urea for excretion through urine. But some ammonia escapes into circulation and is excreted through sweat. When the process is running at high volume, the sweat smell becomes distinctly ammonia-like.
The conditions that drive protein catabolism for fuel are the same ones that produce ammonia sweat.
The Most Common Causes
Endurance Exercise with Depleted Glycogen
This is the most common reason athletes notice ammonia sweat. During long-duration endurance exercise (distance running, cycling, rowing), you progressively deplete your muscle glycogen stores. When glycogen runs low, your body increasingly turns to fat and, to a lesser extent, amino acids for fuel.
The amino acid breakdown produces ammonia, which gets excreted through sweat. The longer the exercise duration and the lower your carbohydrate availability going in, the more pronounced this becomes. Marathon runners, triathletes, and people doing multi-hour training sessions are most likely to notice it.
The fix in this context: carbohydrate availability. Eating adequate carbohydrates before long sessions, and consuming carbohydrates during sessions that last more than 60-90 minutes, reduces the degree to which your body relies on amino acid catabolism.
Low-Carbohydrate and Ketogenic Diets
People following keto or very low-carb diets chronically restrict carbohydrate availability. This shifts metabolism toward fat burning (ketosis) but also increases gluconeogenesis, the process of making glucose from non-carbohydrate sources including amino acids.
If you’re on a keto diet and noticing ammonia sweat, your body is regularly metabolizing protein to make glucose. This is especially likely if your protein intake is high, since more dietary protein means more available amino acids for catabolism.
Options for addressing this:
- Ensure your protein intake isn’t excessive (more protein than your body can use for building and repair goes toward energy or is excreted)
- Keep fat intake high enough on keto that fat is the primary fuel (fat-adapted keto reduces the need for gluconeogenesis)
- Carb timing around workouts even on a low-carb diet (targeted ketogenic diet approach)
Dehydration
Dehydration affects ammonia sweat in two ways. First, when you’re dehydrated, your kidneys conserve water by reducing urine output. This means less ammonia is excreted through urine and more is rerouted through sweat. Second, dehydration concentrates sweat overall, meaning whatever ammonia is present smells more intense.
If you notice ammonia sweat primarily when you haven’t been drinking enough water, hydration is the likely culprit and the fix. Aim for pale yellow urine as a rough hydration indicator; dark urine suggests you need more water.
Very High Protein Intake
If your protein intake significantly exceeds what your body can use for muscle building and repair, the excess amino acids are broken down for energy or excreted. Either way, more nitrogen is processed, more ammonia is produced, and more ends up in sweat.
The sports nutrition guideline for protein intake for active people is roughly 0.6-1.0 grams per pound of body weight per day. Significantly exceeding this, common in some bodybuilding or high-protein diet approaches, can increase ammonia excretion.
When Ammonia Sweat Could Signal Something Medical
The causes above are dietary and exercise-related, not medical concerns. But persistent, strong ammonia smell, especially at rest or with minimal exertion, can indicate kidney dysfunction.
The kidneys are responsible for filtering urea (the non-toxic form ammonia is converted to by the liver) out of the blood and excreting it in urine. When kidney function is impaired, urea accumulates in the blood. Ammonia compounds then show up in higher concentrations in sweat, causing the ammonia smell.
This type of ammonia smell (sometimes described as “uremic fetor”) tends to be:
- Present at rest, not just after exercise
- Not explained by low-carb diet or heavy training
- Accompanied by other symptoms like fatigue, changes in urination, swelling
If you’re noticing ammonia smell in these circumstances, it’s worth getting your kidney function tested (a basic metabolic panel includes creatinine and BUN, the markers for kidney function). This is a straightforward blood test.
Also note: liver disease impairs the conversion of ammonia to urea, allowing ammonia to accumulate. Liver issues can also produce ammonia-related odor, though the full smell profile of liver disease is typically more complex (sometimes described as musty or like rotting fruit).
→ Body Odor Causes: What’s Actually Behind the Smell
Sweat vs. Urine Ammonia Smell
A note on a related but distinct issue: some people notice ammonia smell primarily from urine, not sweat. This can be completely separate. Concentrated urine has an ammonia smell regardless of any medical condition, often just from dehydration or a high-protein diet. If the ammonia smell is from urine and you’re well-hydrated, that’s more worth investigating. If it’s only noticeable when very concentrated first thing in the morning, hydration is almost certainly the answer.
How to Reduce Ammonia Sweat
If you’ve identified a dietary or exercise cause:
Increase pre-workout carbohydrates. For long training sessions, eat a carbohydrate-containing meal 2-3 hours before, or a smaller carbohydrate snack 30-45 minutes before. This tops off glycogen stores and reduces reliance on amino acid catabolism.
Fuel during long sessions. For exercise lasting more than 60-90 minutes, consuming carbohydrates during the session (gels, sports drinks, real food) maintains glycogen and reduces protein catabolism.
Drink more water. More hydration dilutes sweat and supports kidney excretion of urea through urine rather than sweat.
Review protein intake. If your protein intake is very high relative to your training volume and body size, moderating it may help.
Adjust carbohydrate intake on low-carb diets. If you’re following keto or low-carb and the ammonia smell is bothersome, some strategic carb inclusion (particularly around workouts) can help without abandoning the dietary approach entirely.
→ Sweat Odor: Why It Happens, Why Yours Might Be Different, and How to Fix It
The Bottom Line
Ammonia-smelling sweat is almost always a signal from your body about fuel usage: it’s burning protein for energy more than it should be. The causes are usually identifiable, the fixes are clear, and the condition isn’t dangerous in the dietary/exercise context. Where it becomes worth a medical look is when it appears at rest, without dietary explanation, or with other symptoms suggesting kidney or liver involvement. That’s a different situation, and a basic blood panel will clarify it quickly.
Sources
- Protein catabolism and ammonia production during exercise, NCBI PMC
- Urea cycle disorders: biochemical basis and clinical significance, NCBI Bookshelf
- Bromhidrosis (body odor), American Academy of Dermatology
- Body odor and sweating, NHS