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A teacher once told me that after detecting a new scent, you will only be able to smell it for a few minutes.
Is this true? If so, why?
What is the precise length of time one can smell, and does it differ by scent? Also, what "resets" the time--for example, would leaving the room then returning enable one to smell the scent again?
It is true - the process is called habituation. It depends on how frequent (odor exposure [or sniffs] per minute) a smell is registered. Habituation can last from less than ten minutes up to at least 30 minutes (Chaudhury et al., 2010). As mentioned in the link, different parts of the olfactory system appear to be involved, but it is mainly explained through receptor activation on the cell membrane of neurons. There is a limited number of receptors that wait for signaling molecules or odorants (odor molecules) to attach, much like the game musical chairs. Habituation is thought to be more a product of receptor activity at neurons that transfer the information than sensory neurons that receive the odorants. With time, receptors go back to their original states.
Whether this differs by scents depends on several factors. There is great variation in individual scent acuity (see Kandel et al., Principles of Neural Science (5th ed.), ch. 32) from human to human, but frequency of exposure is a likely candidate, as well as salience - how strongly a smell affects us. We are more sensitive to smells that provide an evolutionary benefit by promoting survival, such as the smell of a burning forest. Perhaps habituation is less likely if it does us more harm than good.
This phenomenon is called olfactory adaptation. It basically means that your nose gets adapted to the smell so that you feel like it's not even there. For instance, when you go to the toilet to poop, you don't usually feel the smell and that's because it becomes "normal" for your olfactory system. But when you exit the toilet and reenter in a short period of time, you will feel the smell again. "Olfactory fatigue, also known as odor fatigue or olfactory adaptation, is the temporary, normal inability to distinguish a particular odor after a prolonged exposure to that airborne compound" (https://en.wikipedia.org/wiki/Olfactory_fatigue)
