Reference point
Hold a rusty iron bar in a damp hand for about ten seconds, then smell your palm.
Do this before you read on. An entry only works when you have just smelled the thing.
Fishy-metallic, cold, with a note of blood. Faint but very distinctive, and impossible to confuse.
The surprise of this entry: the smell does not come from the iron. Metal does not evaporate at room temperature. What you smell is the breakdown product of fats on your skin in contact with iron ions — the smell of yourself, created with iron as the catalyst.
That also explains why blood and iron smell alike: both involve a reaction between iron ions and fats.
How to smell it
Wash your hands, leave them slightly damp, and grip a rusty iron bar or a handful of old nails for ten seconds. Let go and smell your palm. Smell the iron bar directly and you will find nothing — which is the proof of the mechanism.
Why this one is hard
Because everyone is convinced they are smelling the metal. The experiment of smelling the bar and then your hand breaks that belief within ten seconds.
Don’t confuse with
This entry
Metallic smell
Smoky & Mineral family
Both are sharp and brief, but their origins differ. The metallic smell is 1-octen-3-one, formed on your skin when iron ions catalyse the breakdown of fats — a biological origin; a match gives inorganic sulphur dioxide from combustion. The metallic smell is damp and metallic, the match dry and sulphurous.
This entry
Metallic smell
Smoky & Mineral family
The metallic smell needs human skin to form — hold a clean iron bar, then smell your hand, not the bar. Hot cement gives off its smell from the material itself and needs no contact.
Scientific note
This mechanism was identified in a study published in 2006, and it overturned the popular understanding of the so-called metallic smell. The compound responsible is 1-octen-3-one, formed when ferrous iron catalyses the breakdown of lipid peroxides already present on human skin. Its detection threshold is among the lowest the human nose can pick up, so a tiny amount is enough to be clear.
In Vietnamese life
This smell is usually named after the object rather than its real origin. We call it the smell of iron because our hand touched iron, just as our ancestors called the smell of rain the smell of rain even though it comes from bacteria in the soil.