Wikia

Demon Skin
Demon Skin 0 yds (Self) range None cooldown 31% of base mana Instant cast Protects the caster, increasing armor by X, and increasing the amount of health generated through spells and effects by 20%. Only one type of Armor spell can be active on the Warlock at any time. Lasts 30 min.
Usable by
Class	Warlock
Properties
Type	Utility
School	Shadow
Cooldown	None
Other information
Ranks	2
Related buff
Demon Skin Increases armor by X, and amount of health generated through spells and effects by 20%. Duration: 30 minutes

Demon Skin is a self-only buff that improves your armor and increases health generated through spells and effects. Lasts 30 minutes.

Rank table

Rank	Armor	Level	Cost
1	90	1	Free^[1]
2	265	10	3

At level 20 warlocks learn Demon Armor which is exactly the same as Demon Skin except it includes more armor. Since only one type of armor self-buff can be used at a time, this spell becomes obsolete once Demon Armor is learned.

For warlocks that start out, this spell should always be maintained. Its long duration means you don't need to recast it that often, but it is easy to overlook an expired buff.

Patch 3.0.8 (2009-01-20): Armor increased by approximately 120%.
Patch 2.4.3 (2008-07-15): Demon Skin is no longer a Magic effect and cannot be dispelled.
Patch 1.6.0 (12-Jul-2005): Now increases health regeneration at all times, as was always intended. Previously, the health regeneration only occurred out of combat. Tooltip updated.