Temporary hit point

Some effects award a character additional, special hit points called temporary hit points. Any damage the characters suffer that would normally affect their real hp applies to their temporary hp first. As their name implies, they don't last forever—only until they're used up or the buff that granted them wears off.

Temporary hp appear as a number with a "+" sign, in parentheses, after the character's real hp count on top of his red hp bar. This temporary HP barrier can be considered an "innermost" defensive layer as inbound attacks still get reduced by all damage reduction you have first (PRR, MRR, Energy Resistance/Absorption, the Stoneskin spell, etc) before you start losing temporary HP. This is in sharp contrast to something like Protection from Elements, a pseudo-temporary HP barrier against several energy types which takes damage before most damage reductions have taken effect.

Bonuses and penalties that affect healing amounts do not affect temporary hit point gains.

Stacking and depletion order

Different sources of temporary HP stack. Temporary HP from the same source don't stack and only the highest value applies. (Aid and Mass Aid are considered the same source and don't stack.)

Temporary hit points are depleted in the same order as they were applied, i.e., first-in, first-out.^{https://www.reddit.com/r/ddo/comments/8mrraj/comment/dzq2ya2/}

Periodically triggering auras

Effects that trigger automatically and periodically are a valued source of protection.

• Brilliance: AoE temporary HP equal to Warlock's Con score (twice as much for epic characters), permanent while Aura-form Eldritch Blast is active.
• Ballad Melody: Greatness: AoE +20 hp or equal to Bard's Charisma score (twice as much for epic characters) (requires Warchanter 4th core), ticking every 10 seconds.

Spells

• Aid: +9-18 hp (depending on the caster level) for 1 minute per caster level
• Aid, Mass: +9-23 (depending on the caster level) for 1 minute per caster level
• False Life: +13-20 hp for 1 minute per caster level. Note that this stacks with the more permanent False Life item enchantment.
• Greater Heroism: +11-20 hp, depending on the caster level, for 1 minute per caster level.
• Heroes Feast
• Reinforce Construct
• Stalwart Pact
• Unstoppable
• Virtue

Class abilities

• Blood Tribute: up to +50/+100/+150 plus 25 per epic level for one minute, has stacking -1 CON debuff until you rest or die
• Boast: up to +100, 8 seconds cooldown.
• Death Eater: Gain HP equal to your Wisdom when you kill an enemy; stacks 3-5 times.
• Feigned Health: equal to 33/66/100% of caster's Charisma score for 3 minutes.
• Flight of Glory: Leap of Faith grants 50 + 3 times character level to caster and nearby allies
• Rage: Barbarian ability (?)
• Jaws of Ice: 10 times your character level for 30 seconds.
• Palliative Admixture: +20 + 2 per Artificer level hp, +10 +1 per two Artificer level temporary spell points for one minute.
• Shining Through: 8x your Constitution Score for 10 minutes.
• Soothing Poultices: equal to 33/66/100% of caster's Intelligence score for 3 minutes.
• Stanch: equal to 50% of your maximum HP for 1 minute, but then adds a -3% maximum HP stacking debuff until you rest or die.
• Vampiric Bond: +20 on hit, 6 seconds cooldown
• Winter's Heart: 8x Wisdom modifier for 30 seconds.

Epic abilities

• Mantle of Sound and Fury: when triggered, +6 per Character Level for 10 seconds.
• Rejuvenation Cocoon: up to 150 hp for 9 seconds
• Spring to Summer
• Undying Vanguard: +10,000 hp for 20 seconds

Item effects

• Angelic Grace
• Bodyfeeder: +15 hp for one minute.
• Concordant Opposition +30 hp.
• Demonic Shield: +30 hp, not removed on rest/quest entrance.
• Feeding
• Legendary Affirmation: 1,000 hp for one minute
• Legendary Concordant Opposition / The Artblade's Gift / The Mummy's Gift
• Lifedrinker: +25 hp for one minute.
• Life Shield: +15 hp for one minute.
• Runic Revitalization
• Soul Eating: +35 hp for one minute
• Titania's Warmth

Other

• Crystallized Unicorn Tear: 5% chance to gain 150 temporary hit points when you are hit.