We all know the acrid mushroom-like metallic smell that comes from metallic utensils, doorknobs, sweaty dumbbells, cutlery, coins and jewelry. It smells of ‘metal’. Except that metal does not smell. We can’t ‘smell’ iron atoms. In fact, when we smell metals we are actually smelling ourselves.
What we smell is actually a type of body odour. When lipid peroxides (which are formed when skin oils oxidise, either enzymatically or with the help of UV light) come in contact with ions of iron with a double positive charge (Fe2+), oct-1-en-3-one is formed, which is the chemical we smell (and is as hard to pronounce as it is to write). Which doesn’t contain any metals at all.
We are the first to demonstrate that when humans describe the ‘metallic’ odor of iron metal, there are no iron atoms in the odors, the odors humans perceive as metallic are really a body odor produced by metals reacting with skin.
-Andrea Dietrich, co-author of “The Two Odors of Iron when Touched or Pickled” as quoted here
It was originally thought that phosphene (PH3) was responsible for the smell. But Dietrich and the rest of her team found that phosphene is, in fact, odourless.
The researchers found that as they increased the amount of Fe2+ in contact with the test subjects’ skin more of these metal-smelling organic compounds formed. Fe3+ ions did not produce any organic compounds.
The skin lipid peroxides and iron ion reaction is also the reason why blood smells a bit like metal, as it contains lots of iron. When you cut yourself, the blood pouring out comes in contact with the chemicals on the skin.
Oct-1-en-3-one can be smelled at very low concentrations. Maybe there is an evolutionary advantage to being able to ‘smell blood’ so easily, as it would be easier to find your prey or your wounded friend.
So remember, next time you think you smell metal, you’re actually smelling yourself and you should maybe go take a shower, or something.
-Francesco (follow me on twitter)
References and further reading
- D. Glindemann, A. Dietrich, H. Staerk, P. Kuschk, (2006) – “The Two Odors of Iron when Touched or Pickled: (Skin) Carbonyl Compounds and Organophosphines” – Angewandte Chemie International Edition
- The smell of money – Science Daily
- Oct-1-en-3-one – Compound Summary – PubChem