Answer: Ketones

Nearly everyone has experienced it at some point: after holding loose change, arcade tokens, or other metal coinage in your hands for a period of time, your hands take on a strong scent most people would describe as metallic (mostly because they’ve associated it over their lives with holding metals).

The smell isn’t the coins rubbing off, however microscopically, on your body. What is really happening is that your body (specifically your skin oils and sweat) are reacting with the iron compounds in the coins and creating new compounds. The perspiration on your skin causes the iron compounds in the coin to gain extra electrons and, in turn, the altered iron reacts with the oil in your skin which then, in yet another reaction, creates a ketone known as 1-octen-3-one (a.k.a. Oct-1-en-3-one). That particular compound, among all the chemistry happening on your skin at the moment of contact with the coin, is specifically responsible for the very strong “metal” scent people associate with holding metal or coins.