Iron is a metallic element that possesses strong supernatural properties, and is thus used by hunters when combating certain supernatural creatures.
Creatures that Iron affects
- Demons- touching iron will burn a demon, they also can't cross iron, much like salt. Their weakness to iron is so strong, that even Azazel, one of most powerful demons ever to exist, who was immune to many other demon weaknesses, was still affected by iron (possibly because it was a Devil's trap). The only known demon immune to Iron is Samhain.
- Ghosts- To be stabbed or shot by iron, will temporarily make the ghost disappear, they also can't cross iron, much like demons. Sam and Dean considered cold iron to be the best way to repel vengeful spirits. If a person possessed by a spirit touches something made of pure iron the spirit will be forced out of the human.
- Hellhounds- Hellhounds can be killed using iron, as demonstrated in the episode "Abandon All Hope..." in which Ellen and Jo sacrifice themselves to destroy the attacking Hellhounds by detonating a propane bomb filled with iron nails and rock salt. (Abandon All Hope...)
- Fairies - All fairies are weakened by iron, although powerful ones like Leprechauns can shrug it off. (Clap Your Hands If You Believe)
- Phoenix - Iron burned the Phoenix's skin, and it couldn't touch Iron, or if imprisoned by it, escape. (Frontierland)
- Leshi - The only way to kill a Leshi, is to cut of its head with an iron axe. (Fallen Idols)
- Shtriga - Iron bullets are the only known thing that can kill a Shtriga. (Something Wicked)
Iron also affects humans who enter full astra state, exactly the same as it does to ghosts, they can be imprisoned by it, to touch it causes them pain and makes them temporarily disappear, although like ghosts, they only reappear inside the iron prison. (Death Takes A Holiday)