Your sweat doesn't actually smell, it's when it mixes with the bacteria on your skin that it releases an odour. Your armpits and pubic regions contain thousands of hairs which then hold on to your sweat and the bacteria.
As James May explains, deodorants work by killing the bacteria on your skin, and they also work as an anti- perspirant by reducing the amount of sweat. The modern anti-perspirant was invented in the 1940s – they contain an active ingredient (almost always an aluminium compound) to reduce the amount you sweat. The active ingredients react with the electrolytes in your sweat to create a thick gel that effectively blocks the top of your sweat glands and contracts your sweat pores. But is this necessarily a good thing, asks May?
By the way, humans aren't alone in smelling, many animals have some serious body odour too. It's not such a bad thing for them, it helps them mark out territory, repel enemies and, most importantly, attract mates.
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