A mildew-like smell coming from a person’s body usually traces back to bacteria breaking down sweat into musty-smelling compounds, though it can also signal a metabolic condition or organ problem. The smell isn’t sweat itself, which is mostly odorless. It’s what happens after sweat meets the microbes living on skin and clothing.
How Skin Bacteria Create Musty Odors
Your skin hosts billions of bacteria, and certain species are especially good at turning sweat into foul-smelling chemicals. The apocrine glands, concentrated in your armpits and groin, produce a thick, protein-rich sweat that bacteria feast on. Corynebacterium is the key player: it breaks down fats in sweat into volatile fatty acids and converts odorless steroid precursors into pungent compounds. Staphylococci and other common skin bacteria contribute by fermenting amino acids and lactic acid into additional short-chain fatty acids.
Several of these byproducts have distinctly musty or damp qualities. Methanethiol, a sulfur compound produced by oral and skin bacteria, is specifically described as having a “putrid, musty smell.” Phenylacetate, another bacterial byproduct, carries a “musty, mousy, sweaty” odor. When these compounds mix together, particularly in warm, moist skin folds where bacteria thrive, the result can closely resemble mildew.
People vary enormously in which bacteria dominate their skin. Two people who sweat the same amount can smell completely different because their bacterial populations differ. Factors like genetics, hygiene habits, antibiotic use, and even the fabrics you wear all shape your skin’s microbial community, which is why some people consistently carry a mustier scent than others.
Clothing Traps and Amplifies the Smell
Sometimes the mildew smell isn’t coming from the person’s skin at all. It’s coming from their clothes. Synthetic fabrics like polyester trap bacteria and their odorous byproducts far more stubbornly than natural fibers like cotton. Sweat-soaked clothing that sits damp in a hamper, gym bag, or washing machine breeds actual mold and mildew, and the musty compounds those fungi produce can survive a normal wash cycle. If someone regularly wears clothes that weren’t fully dried or sat wet too long, the mildew smell transfers to their body and follows them around.
Front-loading washing machines are notorious for developing mildew in their rubber gaskets, which can deposit spores onto clothing during every wash. Towels reused multiple times between washes are another common source. The person may not notice the smell on themselves because olfactory fatigue sets in quickly with constant exposure to your own scent.
Metabolic Conditions That Affect Body Odor
Certain genetic conditions cause the body to accumulate chemicals it can’t properly break down, and some of those chemicals smell musty. Trimethylaminuria is the most well-known example. People with this condition lack a functioning version of the liver enzyme that converts trimethylamine (a compound produced during digestion) into an odorless form. The trimethylamine builds up and gets released through sweat, urine, and breath. The odor is most often described as fishy, but it can also present as musty or ammonia-like, especially at lower concentrations. Eating foods rich in choline, such as eggs, liver, and certain fish, makes the smell worse because choline is a major dietary source of trimethylamine.
Other rare metabolic disorders produce their own signature smells. Isovaleric acidemia causes a “sweaty feet” odor. A deficiency of the enzyme dimethylglycine dehydrogenase leads to a fishy smell through a different chemical pathway. These conditions are uncommon, but if a persistent unusual body odor starts in childhood and doesn’t respond to normal hygiene, a metabolic cause is worth investigating through a urine test.
Liver and Kidney Problems
A musty body odor can be a sign of liver disease. When the liver fails to filter waste products from the blood properly, sulfur compounds like dimethyl sulfide and methyl mercaptan accumulate and get released through the skin, breath, and urine. This produces a distinctive smell that clinicians call fetor hepaticus, described as musty, pungent, and oddly sweet, sometimes compared to rotten eggs mixed with garlic or freshly mown hay. Most people who develop this smell have chronic liver failure, making it a late-stage symptom rather than an early warning sign.
Kidney failure produces its own version. When the kidneys stop filtering urea effectively, ammonia builds up in the blood and escapes through the breath and sweat, creating a bleach-like or stale smell that some people perceive as musty. Both of these organ-related odors come with other noticeable symptoms like fatigue, swelling, nausea, or changes in urine color and volume, so body odor alone is rarely the only clue.
Diet and Supplements
What you eat directly influences how you smell. High intakes of choline, found in eggs, organ meats, soybeans, and many dietary supplements, are associated with a fishy body odor even in people without trimethylaminuria. The mechanism is the same: more choline means more trimethylamine production during digestion, and if the liver enzyme can’t keep up with the load, the excess escapes through sweat and breath. Cruciferous vegetables like broccoli and cabbage contain sulfur compounds that can also contribute to musty or sulfurous body odor when eaten in large amounts.
Alcohol is worth mentioning separately because heavy drinking damages the liver over time, compounding the problem. Even in the short term, alcohol metabolism produces acetaldehyde, which the body expels partly through sweat, creating a stale, slightly sour smell that can read as musty.
What Helps Reduce a Musty Smell
The right approach depends on the cause. For bacteria-driven odor, targeting the microbes is the most effective strategy. Antibacterial soaps or body washes containing benzoyl peroxide applied to the armpits, groin, and skin folds reduce the bacterial populations responsible for breaking sweat into smelly compounds. Antiperspirants containing aluminum salts reduce the amount of sweat bacteria have to work with. Wearing natural fibers, changing clothes promptly after sweating, and drying laundry completely also make a significant difference.
For people with trimethylaminuria, reducing dietary choline and trimethylamine (by limiting eggs, organ meats, and certain seafood) lowers the amount of odor-causing compound the body needs to process. Low-dose antibiotics can reduce the gut bacteria that produce trimethylamine during digestion, though this is a more targeted intervention best guided by a specialist.
If the smell is persistent, doesn’t improve with hygiene changes, and especially if it’s accompanied by other symptoms like fatigue, dark urine, or unexplained weight changes, the underlying cause may be metabolic or organ-related. A simple urine test can screen for trimethylaminuria, and blood panels can evaluate liver and kidney function.