Necrotic damage, or necrosis, results from an attack that rots living tissue, killing flesh, so that it cannot be healed normally. Healing spells and rest have no effect. Necrosis is not a reaction to poison, nor it is a disease; therefore it isn't affected by either neutralize poison or cure disease. If all of the creature's hit points are lost to necrotic damage, the creature is dead and cannot be brought back from death's door, raised or resurrected.
Effective remedies include the spells aid, heal and regeneration. For each of these, the sufferer must be of the caster's religion. Healing salves will heal 1 hit point of necrosis instead of 1-4. Boric serum will transform necrotic damage into ordinary damage.
If necrotic damage is not treated, it will spread, causing 1 additional point of necrotic damage per level, per day, as necrosis attacks biological units, not hit points. This will continue until all necrotic damage is eliminated from the body or the character dies.