system
Given the following post, respond as if you're commenting on Reddit:
human
What is happening when we "get used to" a smell?

Basically, just walked into a public bathroom and someone was taking a poo. When I first started peeing, I couldn't bare the smell. When I was finishing up, I realized I could no longer smell his poo.

What is actually happening for me to not be able to detect the smell as "bad" anymore?
gpt
Your brain getting used to a smell is an evolutionary advantageous trait that allows you to recognize differences in your environment more keenly.

In the same way that human eyes can detect motion from farther distances than a stationary object, the same holds true for the sensation of scent. For scent, strong and highly varying odors will be flagged and highlighted by your brain. It is then up to you to determine and assess whether or not it is actually a hazardous environment for yourself to stay in. If you choose to stay in it, then you have probably figured that the smell of a skunk or the smell of pungent perfume isn't necessarily a harmful environment. Your brain then tones down the highlighting of that smell and dials it down to "get used to" levels such that when another scent comes along, your brain is ready to detect it at a moment's notice and to redetermine if the new environment is healthy environment to stay in.