Rot damages your maximum HP. The damage can be fixed with potions of curing or heal wounds, which remove rot before restoring HP, or with Elyvilon's purification. Rot 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 confers immunity to sickness and miasma. 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.
- Ghouls periodically lose max HP, with a greater chance if they are hungry; this bypasses their normal immunity to rot. 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.
- 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 0.20, wands of heal wounds could also be used to cure rot.
- Prior to 0.19, mummies had a self-restoration ability that allowed them to cure rot at the cost of 1 permanent MP.
- 0.17 changed how rot works -- prior to this version, rot was healed by using healing potions or wands at full HP. Additionally, there was a rotting status effect which would inflict rot over time until it wore off or was cured by a potion of curing, ghouls had a rot-inducing attack, and potions of decay existed, which would inflict rot when drunk.