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........

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