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. Its presence is one of the first things that Sam and Dean often look for at the site of a supernatural event to determine whether demons are involved. 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.