The presence, and especially the smell, of sulfur is closely associated with the presence of demons. There are tales of sulfur-breathing demons, and other demons are thought to live in pits of sulfur and fire in hell.
Sulfur often indicates the presence of demons in Supernatural. Sulfur is such a clear indicator that it is one of the first things that Sam and Dean look for at the site of a supernatural event. It was used in 7.15 Repo Man by Jeffrey to trick Sam and Dean into thinking that a demon is behind a series of murders, when in fact Jeffrey is the killer.
- 1.04 Phantom Traveler - Sulfur is observed on the plane wreckage.
- 1.21 Salvation - John reports that: "Caleb said they found traces of sulfur at Jim’s place", indicating demonic involvement in his death.
- 2.09 Croatoan - the virus is detected through the appearance of sulfur in the blood of infected people, leading the boys to suspect demonic involvement.
- 2.10 Hunted - Sam and Dean find Sulfur on Ava's windowsill after she disappears.
- 2.21 All Hell Breaks Loose: Part One - at the diner when Sam is taken, Dean finds sulfur.
- 3.04 Sin City - Sam finds sulfur at Casey's house.
- 4.09 I Know What You Did Last Summer - Sulfur is found at Anna's house by her parents' bodies.
- 6.01 Exile on Main St. - Dean, under the influence of a djinn, hallucinates a trace of sulfur.
- 6.18 Frontierland - Sam smells sulfur in Samuel Colt's cabin.
- 6.19 Mommy Dearest - Sulfur is found by the bodies of two monster boys, hinting that demons, and therefore Crowley, are involved.
- 8.07 A Little Slice of Kevin - Mrs. Hagar reports smelling sulfur after she witnesses demons kidnapping a child.
- 9.02 Devil May Care - the bus on the naval base smells like sulfur when Sam and Dean investigate it.
- 9.16 Blade Runners - Sam smells sulfur around the Impala after it's been vandalized by demons.
- 9.23 Do You Believe in Miracles? - Sam and Gadreel smell sulfur when they find the First Blade has been removed from its box.
- 11.03 The Bad Seed - the smell of sulfur is reported by witnesses to the attack on the witches at Café Elta.
- 11.06 Our Little World - Sam and Dean smell sulfur in the police station as Len's corpse is wheeled past.
- 12.06 Celebrating the Life of Asa Fox - When Jael invades Asa Fox's house, he leaves behind the scent of sulfur in the living room.
Sulfur and Lore
Sulfur, also called brimstone, is a yellow element that smells strongly of rotten eggs. It has a long association with Hell. Sulfur has been used to treat diseases like eczema, and to kill fungus. It is also a traditional ingredient in black powder.