That sharp, acrid smell reminiscent of a litter box is almost certainly ammonia, and your body produces it as a normal byproduct of breaking down protein. When everything is running smoothly, your liver converts ammonia into urea, your kidneys flush the urea out in urine, and you never notice a thing. But when that system gets overwhelmed or disrupted, ammonia can escape through your sweat, breath, and skin in concentrations high enough to hit your nose like a cat’s spray. The causes range from mundane dietary choices to medical conditions worth investigating, and figuring out which one applies to you is mostly a matter of context.
Ammonia and Why It Smells Like Cat Urine
The reason body odor can mimic cat pee is not a coincidence. Cat urine gets its pungent smell largely from concentrated ammonia and its breakdown products. Human sweat can carry the same compound. Research has established that the ammonia in your sweat comes primarily from ammonia circulating in your blood plasma. When blood ammonia levels rise, sweat ammonia rises with it, and sweat glands essentially act as a release valve for the excess.
This was demonstrated in studies where both healthy subjects given ammonium chloride and patients with liver cirrhosis showed elevated sweat ammonia concentrations that tracked their elevated blood levels.1PubMed. Plasma ammonia is the principal source of ammonia in sweat In other words, your sweat does not create ammonia on its own. It reflects what is already in your bloodstream. Anything that pushes blood ammonia higher will make your sweat smell stronger and more cat-like.
The Keto and Low-Carb Connection
If you recently cut carbohydrates or started a high-protein diet, this is the most likely explanation. When your body runs low on glycogen (stored carbohydrate fuel), it leans harder on amino acids for energy. Breaking down amino acids generates ammonia as waste. Normally the liver keeps up, converting ammonia to urea for your kidneys to handle. But when ammonia production spikes and carbohydrate stores are depleted, the system can fall behind.
Exercise makes this worse. A study comparing low-carbohydrate and normal diets found that after the low-carb diet, both plasma ammonia and sweat ammonia concentrations were significantly higher during sustained exercise. Total ammonia loss through sweat was also greater on the low-carb regimen, likely because reduced carbohydrate stores forced the body to rely more heavily on amino acid metabolism.2European Journal of Applied Physiology. Effect of a low-carbohydrate diet on plasma and sweat ammonia concentrations during prolonged nonexhausting exercise So if you are eating keto and exercising regularly, you have two factors stacking on top of each other. Many people on ketogenic diets report that their sweat and sometimes their breath take on a sharp, ammonia-like quality, and this is the mechanism behind it.
Dehydration amplifies the problem further. Less water means more concentrated sweat, so even a normal amount of ammonia becomes more noticeable. If you are working out in the heat, restricting carbs, and not drinking enough water, the cat-pee smell can become genuinely strong.
When Kidneys Are Not Keeping Up
Your kidneys are responsible for clearing urea, the product your liver makes when neutralizing ammonia. When kidney function declines significantly, urea and ammonia accumulate in the blood. This condition, broadly called uremia, produces a characteristic odor that can show up on the breath, skin, and in sweat. The smell is often described as ammonia-like or metallic.
Earlier research has shown a strong correlation between breath ammonia and blood urea levels in people with chronic kidney disease, with one study finding roughly a tenfold reduction in breath ammonia after hemodialysis sessions.3PubMed Central. Effects of end-stage renal disease and dialysis modalities on blood ammonia level That dramatic shift illustrates how directly kidney function controls the ammonia your body gives off. You do not need to be in full kidney failure to notice a change, either. Even moderate kidney impairment can nudge ammonia levels up enough to alter how you smell, especially combined with dehydration or a protein-heavy diet.
Liver disease is the other side of the same coin. If the liver cannot efficiently convert ammonia to urea in the first place, ammonia builds up regardless of how well the kidneys work. Cirrhosis, hepatitis, and other forms of liver damage can all produce elevated blood ammonia and the body odor that comes with it. The plasma-to-sweat ammonia link documented in cirrhotic patients confirms this pathway directly.1PubMed. Plasma ammonia is the principal source of ammonia in sweat
Rare Metabolic Disorders Worth Knowing About
Two categories of inherited metabolic conditions can produce unusually strong or unusual body odors, and while they are uncommon, they are worth mentioning because they are frequently missed or misdiagnosed for years.
Urea cycle disorders are genetic conditions where the enzymes responsible for converting ammonia to urea do not work properly. Most are caught in infancy, but milder forms can go undetected until adulthood, sometimes surfacing only under metabolic stress like illness, surgery, or a sudden dietary change. A case series of adult-onset urea cycle disorders found that at the time of diagnosis, ammonia levels were elevated in nearly all patients, with values ranging from roughly three to ten times normal concentrations.4PubMed Central. Psychiatric adult-onset of urea cycle disorders: A case-series Symptoms in these adults were often psychiatric rather than the classic metabolic crisis seen in children, including confusion, agitation, and fluctuating consciousness. The body odor aspect tends to be overshadowed by those more dramatic symptoms, but chronically elevated ammonia at lower levels could contribute to persistent unusual sweat and breath odor without triggering a crisis.
Trimethylaminuria, sometimes called fish-odor syndrome, is a different enzyme problem. Here, the body cannot properly break down trimethylamine, a compound produced during digestion of certain foods. The result is a strong odor that people most often describe as rotting fish, but it can also come across as garbage-like, sulfurous, or simply “chemical” in a way that overlaps with ammonia. Trimethylaminuria is caused by mutations in the FMO3 gene and is rare, but milder variants exist where the smell comes and goes depending on what you eat.5JAMA Dermatology. Trimethylaminuria (Fish-Odor Syndrome): A Case Report If your smell is persistent, not clearly tied to exercise or diet, and others can confirm it, asking your doctor about metabolic screening is reasonable.
Bacteria, Skin, and the Smell Factory on Your Body
Your skin hosts a thriving community of bacteria, and these microbes are responsible for much of what we experience as body odor. Fresh sweat is nearly odorless. The smell develops when bacteria break down sweat components into volatile compounds, many of which are acids with sharp, pungent characteristics.
Research on body odor has identified Staphylococcus species as key players in producing acetic acid, isovaleric acid, and sulfur-containing compounds from sweat precursors.6PubMed Central. Understanding the microbial basis of body odor in pre-pubescent children and teenagers Isovaleric acid in particular has a sharp, cheesy, feet-like smell that in combination with ammonia could easily be interpreted as something cat-related. The bacterial composition on your skin varies by body region, by individual genetics, and even by what you have eaten recently, which is part of why body odor is so personal and so variable.
This bacterial dimension explains something frustrating: two people eating the same diet and exercising the same amount can smell very different. One person’s skin microbiome might efficiently convert sweat into relatively mild compounds, while another’s produces a cocktail that registers as ammonia-like or urine-like. Washing with antibacterial soap and keeping skin dry can shift the bacterial balance, but the effect is temporary because the microbial community re-establishes itself within hours.
Your Workout Clothes Might Be the Problem
Sometimes the smell is not coming from your skin at all. It is trapped in your clothing. Synthetic fabrics like polyester are notorious for developing stubborn odors that survive multiple washes. A study comparing polyester and cotton T-shirts worn during exercise found that polyester shirts smelled significantly less pleasant and more intense than cotton ones after the same workout. The difference came down to bacteria: Micrococcus species, which are associated with strong odors, were found almost exclusively on synthetic fabrics.7PubMed Central. Microbial odor profile of polyester and cotton clothes after a fitness session
Polyester fibers are hydrophobic, meaning they repel water but absorb oils and the organic compounds bacteria feed on. This creates an ideal environment for odor-producing microbes to thrive, and the smell compounds can become embedded in the fabric in ways that regular detergent does not fully reach. If your gym clothes or undergarments still smell off even after washing, the fabric itself may be harboring bacterial colonies. Switching to cotton or merino wool, using an enzyme-based laundry detergent, or soaking synthetics in white vinegar before washing can help. Some people find that the cat-pee smell they attributed to their body was actually coming from a synthetic shirt or a pair of leggings that had accumulated months of bacterial residue.
When the Smell Is Not Really There
This is the possibility people least want to consider, but it matters. Phantosmia is the perception of a smell that has no external source. It is an olfactory hallucination, and it is more common than most people realize. The odors people report in phantosmia tend to be unpleasant: burning, chemical, rotting, or urine-like smells are frequently described. Phantosmia can result from infections, traumatic brain injury, neurological conditions, and certain psychiatric disorders.8PubMed Central. Parosmia and Phantosmia: Managing Quality Disorders
A related condition, parosmia, involves distorted perception of real smells. Something that should smell neutral or pleasant instead smells foul. Both conditions can follow viral infections, including respiratory viruses that damage the olfactory nerve. If you smell something cat-like but no one around you can confirm it, or if familiar smells have been off in general, the issue may be neurological rather than metabolic.9PubMed Central. Prevalence and correlates of parosmia and phantosmia among smell disorders This is especially worth considering if the smell appeared after a cold, flu, or COVID-19 infection. Post-viral smell distortion can last months and often improves gradually on its own, though some people benefit from smell training (repeated, deliberate exposure to specific scents to help retrain the olfactory system).
Practical Steps to Figure Out the Cause
Sorting through these possibilities does not require a medical degree. Start with the most common explanations and work outward.
- Check your diet: If you are eating low-carb, high-protein, or keto, try adding moderate carbohydrates back for a week and see if the smell changes. This is the single most common dietary cause of ammonia-heavy sweat.
- Hydrate aggressively: Drink enough water that your urine stays pale yellow. Concentrated sweat smells stronger, and adequate hydration helps your kidneys clear ammonia-related waste more effectively.
- Audit your clothes: Smell your workout gear before you put it on. If it already has a whiff of something off, the fabric is the problem, not your body. Try switching to natural fibers or treating synthetics with enzyme cleaners.
- Ask someone you trust: If you are the only one noticing the smell, phantosmia becomes a real consideration. A blunt friend or partner can confirm whether the odor is detectable to others.
- See a doctor if it persists: Persistent ammonia-like body odor that does not respond to dietary changes, hydration, and hygiene warrants blood work. A basic metabolic panel and kidney function tests can rule out or identify renal issues. If results are normal but the smell continues, your doctor can order more targeted testing for metabolic conditions.
Medications and Supplements That Can Contribute
Certain medications and supplements alter how your body handles nitrogen and ammonia. High-dose amino acid supplements, branched-chain amino acids (BCAAs) popular in fitness circles, and creatine can all increase ammonia production when metabolized. If you started a new supplement regimen around the time the smell appeared, that is worth investigating.
Some medications affect liver or kidney function in ways that indirectly raise ammonia levels. Valproic acid, an anticonvulsant and mood stabilizer, is a well-known culprit: it can inhibit urea cycle enzymes and push blood ammonia up, sometimes substantially. If you are taking a medication that lists liver effects among its side effects and you have developed a new body odor, mention it to your prescriber. The fix might be as simple as a dose adjustment or a switch to a different drug in the same class.
B vitamins in high doses, particularly B6, can also produce strong-smelling urine and occasionally influence body odor. Asparagus famously makes urine smell sulfurous in people with certain genetic traits, and while that is a different compound entirely, it illustrates how directly what you consume shows up in what your body excretes. The general principle is worth remembering: sudden changes in body odor often trace back to something you recently started eating, drinking, or taking.
Why Some People Consistently Smell Stronger Than Others
Even after accounting for diet, hydration, and health, some people simply run higher on body odor than others. Genetics play a role at multiple levels. Your particular mix of skin bacteria is partly inherited, partly environmental. The density and type of your sweat glands vary by genetics and by body region. Your liver’s efficiency at processing ammonia has a genetic component, and the FMO3 gene variants that cause full trimethylaminuria in some people exist on a spectrum. Carriers of a single mutation may never get diagnosed with a disorder but might metabolize certain compounds less efficiently, leading to subtly stronger odor after eating specific foods like eggs, legumes, or certain fish.
Hormonal shifts matter too. Puberty, pregnancy, menopause, and thyroid changes can all alter sweat composition and skin microbiome balance. People frequently report that their body odor changed character during one of these transitions and never quite went back. This is real, not imagined, and is driven by the interplay between hormones, sweat gland activity, and the bacterial communities those conditions favor. If your cat-pee smell coincided with a major hormonal shift, that context is useful information for your doctor.
Stress and anxiety also increase sweating, particularly from apocrine glands concentrated in the armpits and groin. Apocrine sweat is richer in proteins and lipids than the watery eccrine sweat produced during exercise, giving bacteria more raw material to work with. The result is that stress-related sweat often smells different and stronger than exercise sweat. Chronic stress can therefore create a persistent odor issue that has nothing to do with diet or kidneys and everything to do with the type of sweat being produced and where on the body it is concentrated.