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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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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Yeah. Before we all started wearing deodorant, the smell was desirable. It was a good thing to “smell like a man”. We’ve been using deodorant for so long that we’ve been trained to recognize BO as a bad smell now.

Body Odor is the farts from bacteria on your body. Sweat by itself doesn’t have a strong odor. Once bacteria start eating your sweat, they produce the smell we associate with BO. Some people have it worse than others and it’s completely due to their particular microbes. It is specific to them. As for hanging in the air, it is constantly being produced, so if you’re near that person, they need to take a shower or have a giant fan blowing it all away (but it will still be there).

As for an advantage, a lot of the microbes in our bodies are symbiotic. Mostly in our gut. The stuff on the outside isn’t really doing us any good, but it’s also not preventing us from having children. That’s the line in the sand for evolution. It doesn’t have to do us good, it just can’t prevent us from having children, or it will get removed from the gene pool eventually.

Pheromones and our biochemistry is pretty complicated for ELI5… but you may notice some BO more. Has a lot to do with the olfactory bulb and how memory is formed. Before we got all domesticated, BO had more functionality in reproduction.

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.

I dont know the how or why of it all, but someone once told me that a persons body odor smelling pleasant to you signals that you’re near genetic opposites to that person, meaning your offspring would have a variety of genes, making them stronger. Someone that smells bad to you signals that you’re too similar genetically, and wouldnt make strong offspring. I doubt theres any science to back it up, but it hangs in the back of my mind sometimes.