We've all visited friends whose homes smell...well, not so fresh. Or, it might have been your own home that assaulted your senses after you returned from a week away. Regardless, the thought bubble is the same: "How can you not notice such a bad scent?"
Turns out, the home in question might have always smelled like that -- and your brain is to blame for the whole "you not noticing" part. Particularly, the olfactory bulb, which is responsible for interpreting signals from your odor receptors. This is how you smell things. Revolutionary, we know. But this part of your brain is also responsible for determining threats.
In a nutshell, if there is no "threat" associated with a scent, your ability to detect that scent diminishes. You become used to the odor, until you take a prolonged break from the particular scent in question. Find out the full explanation in the video above, along with a very unusual way to get your sense of smell back.