Why do we stop noticing smells?

Greg Jefferis - So, pretty much, any sensory system you can have adaptation and in fact it can be at various levels. People often give the example in introductory classes - your clothes, you tend to forget you're wearing them. Obviously, it will be bad news if you weren't wearing them, but you do tend to forget that sensory experience, after a while, you get used to it. The same with your eyes, you'll get used to the light level in a particular environment and their adaptations within the sensory cells. So, the same is true in most olfactory receptors. And there are also mechanisms downstream within the brain that will modulate your response to particular odours as well.