A musty body odor, often described as stale, damp, or mildew-like, usually comes from bacteria breaking down sweat in warm, moist areas of your body. But the cause isn’t always that simple. Your clothing, hormones, diet, skin infections, and even age-related skin chemistry can all produce or contribute to a persistent musty smell.
How Skin Bacteria Create Musty Odors
Sweat itself is nearly odorless. The smell comes from bacteria that live on your skin, particularly in areas like your armpits, groin, and skin folds. As these bacteria feed on sweat, they break its ingredients into smaller chemicals that evaporate easily and reach your nose. The specific species living on your skin determine what you smell. Corynebacterium and Staphylococcus species break down a protein building block called leucine into isovaleric acid, which has a strong, cheese-like or stale smell. Other bacterial byproducts can smell goat-like, onion-like, or sour.
The balance of bacterial species on your skin shifts over time based on your hygiene habits, the products you use, how much you sweat, and even what you eat. A change in that balance can produce new or stronger odors that seem to appear out of nowhere. If you’ve recently changed deodorants, started exercising more, or moved to a more humid climate, that shift in your skin’s microbial population is the most likely explanation for a new musty scent.
Your Clothes May Be the Source
Before assuming the smell is coming from your body, check your clothing. Researchers distinguish between a “primary odor” originating from the skin itself and a “secondary odor” that develops on garments through separate biological and chemical processes. Clothes left sitting damp in a washing machine commonly develop a musty smell from mold and mildew growth. That odor transfers to your skin when you wear them and can be hard to distinguish from an actual body odor.
Fabric type matters too. Polyester consistently scores worse than cotton for unpleasant odor development, with higher ratings for “sweaty,” “sour,” “musty,” and “ammonia” characteristics. If you wear a lot of synthetic fabrics, switching to natural fibers and making sure laundry dries promptly can eliminate what seems like a body odor problem.
Skin Infections That Smell Musty
A bacterial skin infection called erythrasma can produce a stale or musty odor in skin folds. It’s caused by Corynebacterium minutissimum, a bacterium that infects the top layers of skin. It shows up as irregularly shaped pink or brown patches with fine scaling, most commonly between the toes, in the groin, under the breasts, in armpit creases, and in abdominal folds.
Erythrasma is especially common in people with diabetes, those living in hot and humid climates, and middle-aged women with obesity. It’s frequently mistaken for a fungal infection like jock itch or athlete’s foot, but doctors can distinguish it easily because the infected skin glows coral-red under ultraviolet light. If you have persistent scaling or discoloration in skin folds along with a musty smell, erythrasma is worth investigating. It responds to different treatment than fungal infections, so getting the right diagnosis matters.
Hormonal Changes and Menopause
Hormonal shifts, particularly during perimenopause and menopause, can change your natural scent noticeably. The drop in estrogen during menopause leaves relatively higher levels of testosterone circulating in your body. This hormonal shift can attract more bacteria to your sweat, making it smell funkier than it used to. On top of that, profuse perspiration from hot flashes and night sweats provides extra nourishment for odor-causing bacteria in the armpits and other warm areas.
Other hormonal conditions can play a role too. Hyperthyroidism, endocrine disorders, and hormonal imbalances all increase sweating, which creates the conditions for stronger body odor. If a musty smell appeared alongside other symptoms like heat intolerance, weight changes, or irregular periods, a hormonal cause is worth exploring.
How Aging Changes Body Odor
There’s a well-documented chemical reason why body odor changes with age. A compound called 2-nonenal, which has a musty, grassy, or slightly greasy smell, increases on the skin as people get older. It’s produced when omega-7 unsaturated fatty acids in the skin’s natural oils are broken down through oxidation. This process accelerates with age as the skin’s lipid composition changes, and it’s the primary chemical behind what people sometimes call “old person smell.” It’s not a hygiene issue. Regular washing reduces it temporarily, but because the compound is generated continuously by the skin’s own chemistry, it tends to return.
Diet and Metabolic Causes
What you eat can change what you smell like. High intakes of choline, found in eggs, liver, and certain supplements, are associated with a fishy body odor along with excessive sweating. While this is more fishy than musty, the two descriptions overlap for many people, especially when the smell is faint or mixed with other body odors.
More seriously, liver disease can produce a distinctive musty or sweet-rotten smell known as fetor hepaticus. This happens when the liver can no longer properly filter metabolic byproducts from the blood. The dominant chemicals responsible are dimethyl sulfide, which smells pungent and garlicky, and methyl mercaptan, which smells like rotten eggs or cabbage. Other contributors include ammonia, acetone, and trimethylamine. Fetor hepaticus is a sign of significant liver dysfunction, not an early or subtle symptom. It typically accompanies other obvious signs of liver disease like jaundice, abdominal swelling, or confusion.
Ruling Out Imagined Odor
It’s worth knowing that a condition called olfactory reference disorder involves a persistent belief that you’re emitting an offensive body odor when no actual odor is present. It was recently added to the ICD-11 as a recognized diagnosis. The core features are a strong conviction of having a noticeable body odor, repeated checking or attempts to mask the odor, and social withdrawal because of it. If other people genuinely cannot smell what you’re describing, and the concern is affecting your daily life, this is a real and treatable condition, not something to dismiss or feel embarrassed about.
Narrowing Down Your Cause
Start with the simplest explanations. Smell your clothes before putting them on to rule out laundry mildew. Switch to cotton fabrics for a week and see if the smell changes. Pay attention to whether the odor comes from specific body areas, especially skin folds, which would point toward a bacterial or fungal skin issue.
If the smell is new and you’re over 40, age-related skin chemistry changes or hormonal shifts are common and benign explanations. If the musty smell came on suddenly, is very strong, or is accompanied by other symptoms like skin changes, excessive sweating, fatigue, or digestive problems, it’s worth getting a medical evaluation to check for infections, hormonal imbalances, or metabolic conditions that can alter your scent from the inside out.