The biology of body odour, from sweat glands to skin bacteria
Sweat rarely smells on its own. Body odour develops when bacteria on the skin break down compounds in sweat and release volatile chemicals that evaporate into the air.
This interaction between sweat and microbes explains why some areas of the body smell more strongly than others, why odour varies between people and how deodorants and antiperspirants reduce it.
Sweat is a clear, salty liquid produced by glands across almost the entire surface of the skin. Its production is controlled by the autonomic nervous system, which regulates automatic bodily functions such as temperature and heart rate. The main function of sweat is cooling. When body temperature rises during exercise, stress or hot weather, sweat evaporates from the skin and carries heat away.
There are three main types of sweat gland, each producing slightly different fluids. Eccrine glands sit across most of the body and release a thin, watery sweat made mostly of water and salt. Apocrine glands, found mainly in the armpits and groin, produce a thicker fluid that contains fats, proteins and sugars. Apoeccrine glands, also concentrated in the armpits, produce sweat that is more similar to the watery type but in larger amounts.
Read more: Anhidrosis: why some people – apparently like Prince Andrew – just can’t sweat
Odour develops when bacteria on the skin break down the substances in sweat. The skin naturally hosts many kinds of bacteria. Groups with names such as Corynebacteriaceae, Staphylococcaceae and Propionibacteriaceae are commonly involved. As they feed on sweat, they break its ingredients into smaller chemicals that evaporate easily and reach the nose, creating smell.
Different bacteria produce different scents. Staphylococcus hominis, commonly found in the armpits, creates chemicals that smell similar to onions. Corynebacterium and Staphylococcus epidermidis break down a building block of proteins called leucine into isovaleric acid, a compound produced when bacteria break down sweat that has a strong, cheese-like smell.
Some Corynebacterium species produce compounds often described as goat-like. These smell-producing chemicals can stick to clothing, which absorbs both sweat and bacteria, allowing odours to linger. Research confirms that specific bacteria are linked to characteristic odours.
Armpits and feet tend to smell more strongly because they combine dense sweat glands with warmth and moisture, creating favourable conditions for bacterial growth.
Washing removes sweat and reduces bacterial numbers, helping to limit odour. Changing clothes after heavy sweating is also important, as fabrics can trap sweat and microbes. Regular bathing and clean clothing reduce the build-up of odour-causing compounds.
Some people sweat excessively without heat or exercise. This condition, known as hyperhidrosis, affects around 2% of the population and often requires medical treatment rather than improved hygiene alone. Treatment options include prescription-strength antiperspirants, medications that reduce nerve signals to sweat glands, botulinum toxin injections, and iontophoresis, a treatment that uses a mild electrical current passed through water to temporarily reduce activity in sweat glands. In severe cases, surgery may be considered.
Read more: 7 things you can do if you think you sweat too much
Deodorants and antiperspirants tackle odour in different ways. Deodorants mainly target bacteria, using antimicrobial ingredients to slow their growth and fragrances to mask residual smells. Some plant-based products contain substances such as tea tree oil, potassium alum or pentagalloyl glucose, which also have antimicrobial effects.
Antiperspirants reduce the amount of sweat reaching the skin. Aluminium salts, such as aluminium chlorohydrate, form temporary plugs in eccrine sweat gland openings, limiting moisture and reducing the resources bacteria need to produce odour. Many products combine both approaches.
Body odour varies between people and can be influenced by genetics, age, diet, stress and health conditions. Food and drink can also play a role. Compounds from garlic, onions and some spices can circulate in the bloodstream and be released through sweat, altering its smell. Alcohol is partly excreted through breath and skin and can increase sweating, giving bacteria more material to break down.
Medications can affect body odour in similar ways. Some increase sweating, while others alter metabolism or change the balance of bacteria on the skin. Antibiotics, for example, can shift microbial communities, and certain antidepressants and diabetes medications may increase perspiration. These changes are usually temporary.
Men generally have larger sweat glands and tend to produce more sweat, which can support larger bacterial populations and higher levels of volatile fatty acids such as isovaleric acid, a compound produced when bacteria break down sweat that has a strong, cheese-like smell.
Read more: The dirty truth about what’s in your socks: bacteria, fungi and whatever lives between your toes
Occasionally, changes in body odour signal an underlying condition. Trimethylaminuria is a rare inherited disorder in which the body cannot properly break down trimethylamine, resulting in a strong fish-like smell. There is no cure, but symptoms can often be managed through diet, specialised soaps, antibiotics that reduce certain gut bacteria and supplements that can help limit production of the chemical.
Other medical conditions can also alter body odour. Uncontrolled diabetes can produce a sweet or fruity smell on the breath, liver disease can cause a musty odour, and advanced kidney disease may lead to a urine-like smell. Certain infections and metabolic disorders can also change how the body smells.
For example, researchers have investigated whether analysing volatile chemicals released from the body could help detect infections such as malaria. One study examined whether odour profiles might assist diagnosis through chemical signatures in breath and skin emissions.
Sweat remains essential for regulating body temperature. It does not meaningfully remove toxins, despite common claims. Detoxification is carried out primarily by the liver and kidneys. This means you cannot “sweat off” a hangover or “sweat out” a cold. Alcohol is broken down by the liver, and viral infections are cleared by the immune system, not through sweat.
Read more: The truth about detoxes – by a liver specialist
However, prolonged sweating during intense exercise or hot weather can lead to fluid and electrolyte loss. To prevent dehydration, it is important to drink enough fluids, and during sustained exertion drinks containing electrolytes may help replace what has been lost.
Body odour is not simply a matter of cleanliness. It reflects the complex interaction between sweat glands, skin bacteria, clothing, diet, medication and individual biology. For most people it is manageable and normal. In some cases, persistent or unusual changes in smell may warrant medical advice.
Strange Health is hosted by Katie Edwards and Dan Baumgardt. The executive producer is Gemma Ware, with video and sound editing for this episode by Anouk Millet. Artwork by Alice Mason.
In this episode, Dan and Katie talk about a social media clip via YouTube from Alexandrasgirly.
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Primrose Freestone does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.