A creature with this special quality ignores damage from most weapons and natural attacks. Wounds heal immediately, or the weapon bounces off harmlessly (in either case, the opponent knows the attack was ineffective).
The numerical part of a creature’s damage reduction (or DR) is the amount of damage the creature ignores from normal attacks. Usually, a certain type of weapon can overcome this reduction. This information is separated from the damage reduction number by a slash. For example, DR 5/magic means that a creature takes 5 less points of damage from all weapons that are not magic. If a dash follows the slash, then the damage reduction is effective against any attack that does not specifically ignore damage reduction.
The most common forms of damage reduction can be overcome by any magic weapon (DR/magic), a certain type of weapon damage (piercing, bludgeoning, or slashing), a special material (adamantine, silver, or cold iron), or strongly aligned attacks (good, evil, lawful, or chaotic).
Some creatures can be harmed by more than one kind of weapon while others require combinations of weapon properties to be harmed. For example, a creature with “DR/magic or cold iron” could be harmed by any magic weapon or any weapon made of cold iron while a creature with “DR/magic and cold iron” can only be harmed by a weapon that is both magical and made of cold iron.
Damage reduction does not protect against damage from energy attacks (even nonmagical ones) or untyped damage from esoteric effects; however, when a spell, spell-like ability, supernatural ability, or other esoteric effect deals bludgeoning, piercing, or slashing damage or specifically deals weapon damage, that damage is subject to damage reduction.
Whenever damage reduction completely negates the damage from an attack, it also negates most special effects that accompany the attack, such as injury poison, a monk’s stunning, and injury-based disease. Damage Reduction does not negate touch attacks, energy damage dealt along with an attack, or energy drains. Nor does it affect poisons or diseases delivered by inhalation, ingestion, or contact.
Attacks that deal no damage because of the target’s damage reduction do not disrupt spells.
Stacking Damage Reduction
If a creature has damage reduction from more than one source, the two forms of damage reduction stack using the following rules:
- Each type of damage reduction must come from a different type of source. Specifically, you can have one source of damage reduction from your race (or template), one from equipment (such as armor), one from an esoteric effect (regardless of magical system), and any miscellaneous sources that explicitly state that they stack with other sources or increase the amount of one of these existing sources. (Note that magic items that provide DR as a magical effect count as an esoteric effect, not as equipment.)
- Damage reduction must be the same type or DR/— to stack. E.g. DR/adamantine will stack with other instances of DR/adamantine but not with DR/good or DR/cold iron.
- You get the benefit of the best damage reduction in any given situation.
So, for example, let’s consider an evil ousider whose race has DR 5/magic and good. It wears Half Plate armor made of adamantine for DR 5/— (DR 3/— plus DR 2/—, as adamantine explicitly improves the existing DR of the armor), casts the stoneskin spell (DR 10/adamantine), and manifests the biofeedback power (DR 2/—).
First, let’s look at the sources: Race (DR 5/magic and good), Equipment (DR 5/—), and Esoterica (DR 10/adamantine; DR 2/—).
The highest damage reduction that this example can have is DR 15. the DR 5/— from Equipment will stack with everything else. The DR 5 from Race and DR 10 from Esoterica do not stack, because they have different types (good and magic vs adamantine). The race DR would stack with biofeedback though for DR 7; however, this is still less than stoneskin grants, so it will be using that spell in most instances. This creature would ignore the first 15 points of damage from any attack that doesn’t overcome its DR.
If it is attacked by someone wielding an adamantine sword, then the damage reduction will drop to 12 (DR 5/magic and good + DR 5/— + DR 2/—). If the adamantine sword were also enchanted with a +1 enhancement bonus and was good-aligned, the creature’s damage reduction would drop to 7 (DR 5/— + DR 2/—). On the other hand, if attacked with a +1 good-aligned sword that were not made of adamantine, the creature would still benefit from the full DR 15, as neither the DR 5 from its equipment nor the DR 10 from stoneskin is overcome by magic or good-aligned weapons.