What does metal objects smell like and why?

Most metals are described as odorless substances. Is it really so? And if so, where does the distinctive smell of metal coins, keys, nails and tools come from?

To understand the problem with smelling metal, one must realize how the mechanism of the sense of smell works.

It is related to registering chemical compounds present in the air. When we inhale nitrogen and oxygen, we also draw in other molecules deposited on moist cilia deep inside the nose. These cilia interact with olfactory receptors, resulting in information being sent to the corresponding sector of the brain.

Accordingly, for the sense of smell to work, the molecules of a substance must remain suspended in the air. The more molecules are suspended in the air, the stronger the scent. Therefore heat, humidity or evaporation facilitate the separation of molecules and at the same time intensify our sensations. No wonder then that we can smell a mug of freshly brewed coffee more easily than a drink that has long since cooled down.

With metal, the situation is exactly the opposite. While hot coffee or soup generously spreads aromatic particles, almost nothing comes off metal. Sniffing a piece of sheet metal will not draw in too many particles, and you should not smell anything.

And yet, bringing our nose close to coins or keys, we usually register a characteristic "metallic" smell. Maybe not very intense, but still some. Of course, you don't have to be an expert to deduce that the slight odor comes not from the metal itself - after all, money doesn't smell - but from the substances coating it.

In recent years, their composition has become the subject of interest of, among others, chemists from Virginia State University and the University of Leipzig. The Americans and Germans have come to the conclusion that the smell of sniffed coins has to do with humans themselves. Sweat, sebum and other skin secretions are deposited on the objects we touch, interacting with the metal.

For example, body contact with the surface iron or copper causes oxidation and the formation of ions that break down the lipids contained in sweat. The resulting chemical compounds (mainly C8H14O) are the actual source of many groped objects' "metallic" smell.

It is worth mentioning that similar substances (and therefore the metallic smell) can be found in other places where organic substances come into contact with iron atoms - for example, in blood.