Double-tapping the fire button causes Isaac to sneeze blood, dealing damage to enemies in front of him. The sneeze deals damage equal to 1.5x Isaac's damage, knocking enemies and projectiles back. Knocked back enemies take 10 additional damage if they hit a wall or obstacle. If the knocked back enemies hit other enemies, those additional enemies take 10 damage.
The sneeze has a cooldown of 1 second.
The reflected projectiles deal 6 damage to enemies if it would have caused Isaac half a heart of damage, and 7 damage if it would have caused Isaac a full heart damage.
The sneeze applies a curse to enemies. Enemies under the curse will take more damage from Brimstone-like laser attacks and violently explode on death, damaging and spreading the curse to nearby enemies. Any enemies spawned by those under the curse will also be cursed.
The following attacks will deal increased damage (2x damage +3 flat damage):
Tainted Azazel begins with an inherent version of Hemoptysis that allows him to deal full damage to cursed enemies.
The innate sneeze ability is entirely separate from Hemoptysis, and so the sneeze can be triggered twice in quick succession. However, triggering the sneeze from Hemoptysis will cancel Tainted Azazel's brimstone charge, meaning that this item is largely ineffective as this character.
The sneeze's range is affected by the shot speed stat, and not by the range stat itself.
The sneeze can push Bombs, pickups and enemy shots.
The collision damage can be used to damage Hosts while their skulls are lowered.
Brimstone lasers shot by enemies who are not charmed, such as Monstro II, will also do increased damage to cursed enemies
Revelation's charged attack will not deal increased damage to cursed enemies
Synergies
Fire Mind: The sneeze will still set enemies on fire, but not cause explosions, similar to its interaction with Brimstone.
Loki's Horns: Chance to sneeze in all cardinal directions.
Monstro's Lung: Multiple sneezes are applied around the character.
The Wiz: Shoots two sneezes diagonally instead of one straight forward.
Ipecac: The sneeze causes an explosion. The explosion deals additional damage equal to 3x Isaac's damage +10 and will not hurt Isaac.
Brimstone-like laser attacks and violently explode on death, damaging and spreading the curse to nearby enemies. Any enemies spawned by those under the curse will also be cursed.
Azazel/ 
Tainted Azazel
Athame
Brimstone Bombs
Head of Krampus
Lil Abaddon
Lil Brimstone
Maw Of The Void
Montezuma's Revenge's brimstone (not tears)
Mega Blast
Shoop da Whoop!
Trisagion
Bombs, pickups and enemy shots.
Hosts while their skulls are lowered.
Monstro II, will also do increased damage to cursed enemies
Revelation's charged attack will not deal increased damage to cursed enemies
Fire Mind: The sneeze will still set enemies on fire, but not cause explosions, similar to its interaction with 
Loki's Horns: Chance to sneeze in all cardinal directions.
Monstro's Lung: Multiple sneezes are applied around the character.
The Wiz: Shoots two sneezes diagonally instead of one straight forward.
Ipecac: The sneeze causes an explosion. The explosion deals additional damage equal to 3x Isaac's damage +10 and will not hurt Isaac.
Tainted Azazel Unlocks 
Delirium Unlocks 
The Binding of Isaac: Rebirth
