Rot damages your maximum HP. The damage can be fixed with curing or heal wounds, which remove rot before restoring HP, or with Ely's purification. It effectively reduces the effectiveness of healing until cured.
All undead, nonliving, demonic, holy, and insubstantial species and monsters are immune to rotting attacks, as are Gargoyles and Vine Stalkers. This also makes them immune to sickness and miasma. (Ghouls' periodic rotting and undead rotting-instead-of-mutation effects ignore rot resistance.) Zin's Vitalisation, Dithmenos' Shadow Form, Statue Form and Necromutation also grant immunity to rotting attacks, and demonspawn with the Foul Stench mutation eventually gain rot resistance.
Sources of Rot
Rotting can be inflicted by:
- Miscasting Necromancy spells (and by extension, possibly from Zot traps, Hell effects, and acts of Xom)
- Attacks from necrophages and death oozes.
- Advanced mummies' death curses may inflict rot.
- Quaffing a potion of decay.
- Ghouls periodically lose max HP, with a greater chance if they are hungry. They can restore current and max HP by eating chunks.
- Standing in miasma without rotting resistance has a 50% chance to drain 1 max HP every turn you do so. It also poisons and slows you. Poison resistance only protects against the poison effect.
- Attempting to mutate the undead (mummies, ghouls, lower-satiation vampires and lichform characters) causes decomposition, which rots max HP, as well as possibly draining stats. It can be blocked by an amulet of resist mutation with a 90% chance.
Curing Rot Damage
The damage can be fixed by potions of curing, potions of heal wounds, a wand of heal wounds, or by invoking Elyvilon's purification. Ghouls can restore rotted HPs by eating meat. Mummies, who cannot consume potions, must rely on wands of heal wounds and their Self-Restoration ability.
Crawl used to have a "rotting" spell, which caused the flesh of all those near the caster to rot. It affected the living and many of the corporeal undead.
Prior to 0.17, ghouls had a rotting attack.