Catching actual molecules
How Does Smelling Work?
Smelling means molecules from an object physically reaching receptors in your nose.
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Step 1 of 5
Smells are real molecules travelling.
Bits of the object genuinely break away and float to you. Smelling bread means bread molecules are physically inside your nose.
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Step 2 of 5
Receptors recognise molecule shapes.
High in your nose sit around 400 types of receptor, each responding to particular molecular shapes. A molecule fits, and the cell fires.
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Step 3 of 5
Combinations give the variety.
One smell activates a particular set of receptors. With 400 types, the number of distinguishable combinations runs into the trillions.
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Step 4 of 5
The signal goes almost straight to memory.
Smell connects directly to the brain's memory and emotion regions, bypassing the relay other senses use. That is why a smell can floor you with a memory.
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Step 5 of 5
Most of taste is really smell.
Your tongue detects only a handful of basic tastes. Flavour is mostly odour reaching your nose from inside your mouth — which is why food is dull with a cold.
Dogs have hundreds of millions of receptors to our few million, and far more brain devoted to processing them.
The short version
Smell works by molecules physically reaching receptors in your nose, and the pattern they trigger is the smell.
Try it yourself
Hold your nose and eat a jelly sweet. You get sweetness but no flavour until you let go.
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