Has this ever happened to you? You walk into a room and smell something. You stay in the room, and notice that you can't sense the odor any more. But then someone else walks in, and says "Hey! What smells in here?" Why does that happen? Why does your nose become less sensitive?
You smell an odor when the molecules from the smelly stuff reach special spots in your nose called receptors. The odor molecules fit into the receptors like a key in a lock. Basically, when all of the receptors are full, you can't smell that same scent any more. You may even think that it is gone. But when someone with unblocked sensors walks in, he or she can detect the odor right away.
Here's an activity that will let you test how fast your receptors get blocked. Find a bottle of something that smells nice (perfume or mouthwash works well). The bottle should have a cap that can be opened and closed quickly. Open the bottle and take a whiff. OK! Now close the bottle. Count to ten, then open and take another sniff. Does it smell as strong? Close, count, and repeat. Keep going until you can hardly even smell the stuff in the bottle. Now wait about ten minutes and smell again. That should be enough time for the odor molecules to clear out of your receptors, allowing you to get the full effect. If you find this interesting, you can repeat but wait different amounts of time between sniffs.
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