Fresh sweat is nearly odorless. The smell you associate with sweating is actually produced by bacteria on your skin breaking down compounds in sweat into pungent byproducts. The specific bacteria living in your armpits, the type of sweat glands involved, your genetics, and even the fabric you’re wearing all shape how strong that smell gets.
Two Types of Sweat Glands, Very Different Outputs
Your body has two main kinds of sweat glands, and they produce very different fluids. Eccrine glands cover most of your body and release a watery solution made up of water, sodium, potassium, and small amounts of urea and ammonia. This is the sweat that cools you down during exercise or in the heat, and on its own it’s essentially odorless.
Apocrine glands are concentrated in your armpits and groin. They secrete an oily substance rich in proteins, lipids, and steroids. This fluid is also odorless when it first leaves the gland, but it’s packed with the raw materials bacteria need to produce smell. Apocrine glands don’t activate until puberty, which is why young children rarely have noticeable body odor. Rising androgen levels during puberty trigger apocrine gland development, and “adult-type” underarm odor follows.
Bacteria Turn Sweat Into Smell
The real source of body odor is your skin’s microbiome, particularly the bacteria thriving in the warm, moist environment of your armpits. Two bacterial groups do most of the damage: Corynebacterium and Staphylococcus species. People with stronger body odor consistently have a higher proportion of Corynebacterium in their underarms.
These bacteria break down the proteins and lipids in apocrine sweat into volatile compounds that your nose picks up easily. The two main categories of odor molecules are volatile fatty acids and thioalcohols. Volatile fatty acids produce the classic sour, sweaty smell. Thioalcohols are present in only trace amounts but are far more pungent, contributing a sulfurous, onion-like quality. A specific enzyme in the bacterium Staphylococcus hominis is responsible for releasing the most abundant thioalcohol from sweat precursors.
Corynebacterium species, meanwhile, use a zinc-dependent enzyme to release branched fatty acids from sweat. One of these, a compound called E3M2H, has been described as having a very strong, pungent odor and is considered a signature molecule of underarm smell.
Genetics Play a Bigger Role Than You’d Think
A single gene called ABCC11 has an outsized influence on body odor. A specific variant of this gene dramatically reduces the amount of odor precursors secreted by apocrine glands. Between 80 and 95 percent of people of East Asian descent carry this variant, which is also associated with dry, white earwax. Among people of European and African descent, only 0 to 3 percent carry it. If you’ve ever noticed that some people seem to barely produce underarm odor no matter what, genetics is likely the explanation.
The same gene variant is also strongly linked to whether someone develops bromhidrosis, the clinical term for chronically strong body odor. People with wet earwax (the non-reduced-odor variant) are far more likely to experience it.
Foods That Change How You Smell
What you eat can alter your body odor through both eccrine and apocrine pathways. Garlic, onion, curry, and alcohol are the most well-documented culprits. These foods contain sulfur compounds or other volatile molecules that get absorbed into the bloodstream and eventually excreted through sweat, where bacteria process them into noticeable smells.
Red meat, egg yolks, and soybeans are rich in choline, betaine, and L-carnitine, which gut bacteria convert into trimethylamine (TMA). Your liver normally neutralizes TMA, but in large quantities or in people with reduced liver enzyme activity, excess TMA can be excreted through sweat, breath, and urine, producing a fishy odor. In its extreme form, this becomes trimethylaminuria, a rare genetic condition (affecting roughly 1 in 200,000 to 1 in 1,000,000 people) where a liver enzyme deficiency causes persistent fish-like body odor.
Your Clothes Make a Difference
The fabric you wear directly affects how much odor builds up. Polyester is significantly worse than cotton. In a study comparing clothing worn during exercise, polyester shirts smelled more intense, more sour, more musty, and more ammonia-like than cotton shirts worn during the same workout. The reason comes down to which bacteria each fabric supports.
Polyester promotes the growth of Micrococcus species, odor-producing bacteria that reached populations of up to 17 million colony-forming units per square centimeter on polyester fabric. Cotton showed practically no selective growth of these bacteria. Cotton did support Staphylococcus and Propionibacterium growth, but these produce less pungent compounds. If you’ve noticed your gym shirts smell worse than your cotton t-shirts even after washing, the fabric itself is likely harboring a different bacterial community.
Medical Conditions That Worsen Body Odor
Several health conditions can amplify body odor beyond what’s typical. Obesity creates more skin folds where moisture and bacteria accumulate. Diabetes can alter sweat composition. Hyperhidrosis (excessive sweating) provides more substrate for bacterial breakdown. Skin conditions like erythrasma and trichomycosis axillaris involve bacterial overgrowth directly on the skin or hair that intensifies smell.
Eccrine sweat, which is normally odorless, can develop a smell when excessive moisture softens the outer layer of skin (keratin), and bacteria degrade that softened keratin into foul-smelling compounds. This is one reason feet develop a distinctive odor even though they have eccrine glands rather than apocrine ones: the enclosed, damp environment of shoes creates ideal conditions for bacterial breakdown of softened skin.
How Antiperspirants and Deodorants Work
Antiperspirants and deodorants tackle body odor through completely different mechanisms. Deodorants use antimicrobial agents or fragrances to reduce bacteria or mask smell. Antiperspirants go after the sweat itself.
Antiperspirants contain aluminum salts that interact with proteins in your sweat to form a gel plug inside the sweat pore. This plug physically blocks sweat from reaching the skin surface. The process happens in two stages: first, the aluminum ions interact with sweat proteins at a specific pH to form tiny insoluble complexes that attach to the walls of the sweat duct. Then these complexes collect more protein molecules and expand until the duct is fully blocked. By keeping the skin dry, antiperspirants eliminate the food source bacteria need to produce odor.
For people whose body odor doesn’t respond well to standard products, the underlying bacterial population may be the issue. Someone with a Corynebacterium-dominant underarm microbiome will generally produce stronger odor than someone whose armpits are colonized primarily by Staphylococcus epidermidis or other less odor-producing species. Shifts in this bacterial balance can happen with changes in diet, stress, medication, or even the products you use on your skin.