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Your sense of smell often notices changes before you can see them. It can detect smoke before flames are visible, spoiled food before it looks different, or gas leaks before they become obvious. Smell is closely connected to the parts of the brain responsible for memory and emotion.
That's why certain scents can instantly remind you of people or places from years ago. Your nose is constantly scanning the air without you realizing it. It's one of your body's earliest warning systems.
© National Institute on Deafness and Other Communication Disorders