Eli5: why does our brain tell us that some smells are good, flowers, and some smells are bad, pig pen.
In: Biology
Usually it’s a matter of how it would help or hurt our safety. Bad smells are often things which are toxic or infectious – nasty chemicals, rot, defecation. Good smells are things like good food, sweet fruit (which is similar to the smell of flowers), clean fresh air.
Our smell receptors serve a very important purpose. Generally things that smell good are okay for us. And on the other hand, things that smell bad could be bad for us. Poop, rotten meat, bad bacteria growth, etc. it’s almost like an alert and detection system for us.
Many unpleasant smells help us to identify things that are dead and dying. This is useful when trying to figure out if food is still good to ear or not. By developing a negative reaction to rotten food, we’re less likely to eat is and thus less likely to become ill from it.
There are two reasons. One is instinct. The brain just classifies some smells as good and others as bad because over the course of millennia it was useful for smells to be classified as such. This is why things that could possibly spread disease, such as rotting meat and feces, smell bad.
The other reason is a learned response developed throughout each person’s lifetime. It’s very common for people to like certain smells that others consider neutral or just mildly pleasant if they have some positive experience or nostalgia associated with the smell.
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