For example you open a new air freshener and you smell it and it lasts for a few days but does your nose ‘get used’ to the fragrance and you stop smelling it?
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Sense of smell is based od chemical reactions with a particke in air. So longer one of detectable particles are in air less and less reagents there is to detect and we run out of it after some time
Although there is something to be said about the amount of chemicals present in the air, and thsnkuffly the other commenters did. This is however, also a biology question.
What you’re describing is called olfactory fatigue, also known as nose blindness. It is a phenomenon, that prolonged exposure to specific smells causes a lack of its perception. When you apply perfume, you smell it for a few minutes, but after some time, people around you can smell it and hopefully complement you, but you can’t smell it anymore. The same goes with unpleasant odors.
Noseblindness comes from a negative feedback loop that basically prevents further sensation of the smell. This is basically a built-in limiter that works in a complicted way to prevent further sending of electrical impulses to the olfactory cortex.
If you have further wuestions, please ask.
The olfactory receptors we have are phasic in nature, which means that the neurons give response ONLY when there is a change in the signal. So once there is a new smell, you smell it, but since it doesn’t change anymore the neurons won’t activate. The moment you leave the room to experience new smells, the neurons activate again.
Noses aren’t great at picking up static smell but are great at detecting changes in smell. Like when you go on vacation for awhile, you’ll notice a smell about your house that youre accustomed to. People who smell like body oder or cigarettes constantly don’t know how bad they smell to clean people or non smokers.
Our brains tend to tune out nerve signals they receive continously. Otherwise you wouldn’t get anything done, because the feeling of wearing socks, a slightly itchy scalp, the taste in your mouth, the tiniest background noises and a thousand other small things you could technically notice would all fight for your attention and drive you out of your mind.
The sense of smell is a bit like a key in a lock, the smelly molecules are normally large complicated molecules and the sense receptors are like holes where the molecules can settle in if they are the right shape. If a right shaped molecule settles in a receptor you get a message about the smell. Your brain is geared up to getting new information, existing information isn’t going to be a threat to you so is less important than new stuff. With smells over time all the receptors may become full or the brain ignores existing information.
A lot of people did a great job explaining the biological part of your question. There’s also a psychological aspect, though.
Things you experience a lot (like smells, sounds, etc.) are blocked out by your brain. It’s used to them, and doesn’t find them interesting. It’s why farmers aren’t bothered by the smell of manure. They’re so used to it that their brain blocks it out.
The biological part explained in other comments applies when you’ve been around the smell for a short, continuous while. The psychological aspect (called habituation) applies when the smell or sound is recurring.
In general, none of your senses detect *things*. Instead, they detect *changes* in things. That’s why a pool feels cold at first (the temperature around your skin just changed), but then you don’t feel it any more after a while (nothing is changing anymore).
So: you smell the air freshener when you spray it (the scent in the air has changed), but if it’s constantly in the air then you’ll stop smelling it (nothing is changing).
The way it was described to me is that the brain is a “difference engine”. It works, in part, by recognizing when things in our environment change.
Sense of smell in the wild is a survival sense. It can lead you to food, or it can warn you of danger. If you’re out meandering the wild and come across the rotting carcass of an animal, that’s going to be a pretty strong scent. And if your brain wasn’t able to filter it out after a short while, any sufficiently strong scent would be enough to defeat your sense of smell’s ability to inform you about your environment.
In other words, if you rely on scent to survive, having your sense of smell defeated by strong odors is not going to support Darwinian logic. Your body has made you aware of the strong odor and then adapts so that you can still pick up other scents without being overpowered by the loudest stink in the room.
This goes with every sensory perception you have by the way:
1. New sensations always feel the strongest
2. If you felt the same way each time, you would be in a constant state of “oh no! What is that? Fight or flight?”
3. Ie. Jumping into a pool of cold water. If your brain did not desensitize you to this perception, you would be constantly in a state of shock.
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