What is body odor and why does it seem to “hang” in the air? Why is it so profound in some individuals? Was there an advantage to this?
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You have 2 kinds of sweat glands: eccrine, which are all over the body, release water-based sweat directly to your skin, and don’t really have a strong odor. And apocrine glands, which are concentrated in certain areas–underarms, groin, feet, scalp, plus small amounts by the eyes and ears. They release an oil into your hair follicle that bacteria like and the bacteria live in those areas, surviving off of that oil. They digest it and release a waste product, and that waste product is smelly. That’s body odor. But why? Dunno. Most other mammals have apocrine glands all over their body, it’s just humans that have them only in certain areas where there is a lot of hair, though some great apes are going in that direction, too. Basically, it looks like in humans, the eccrine glands took over almost all of the responsibility for temperature regulation, but in other mammals, the apocrine glands play the main role. Interestingly, in dogs, it’s kind of reversed–dogs have apocrine glands all over but only have eccrine glands in their nose and paws, which is why their nose is cold and moist.
Anyway, men tend to have more apocrine glands than women, which might be why some men can seem smellier. A significant percentage of people from east and southeast Asia and to a lesser extent native Americans have apocrine glands that don’t secrete the oil that bacteria like, so they don’t have the smelly bacteria waste product, so their body odor will be much reduced from people without that allele. So if there’s an advantage to having body odor, it’s not a universal one and natural selection appears to have caused it to be lost in a significant percentage of humans.
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