Hit points

A character's hit points (or HP) reflect their current healthiness and durability, and are displayed in an X/Y format; the X shows your current hit points, while the Y shows your maximum. Monsters, traps, and a wide variety of other effects will all reduce your current HP, but this recovers over time unless you are sick. Your max HP only changes under rare circumstance:

• Gaining an experience level will raise your max HP by an amount dependent on your species.
• Improving your Fighting skill will increase max HP slightly.
• Gaining the Robust mutation increases your max HP by 10% per rank.
• Rotting attacks will reduce your max HP by small amounts (but this can be cured by quaffing a potion of curing or potion of heal wounds when at full HP, by zapping yourself with a wand of healing when at full HP, or by using a mummy special ability).
• Casting Borgnjor's Revivification permanently reduces your max HP by a small amount.
• Gaining the Frail mutation reduces your max HP by 10% per rank.

The formula is:

 Max HP = (Racial Mod.) * (Mutations Mod.) * (Forms Mod.) 
                        * (HP Background Bonus + 11*XL/2 + Fighting*XL/8)

The racial modifiers can be looked up in this table:

Species	Modifier
Felid	0.6
Spriggan	0.7
Deep Elf, Tengu, Kobold	0.8
High Elf, Sludge Elf, Halfling, Octopode	0.9
Human, Demonspawn, Merfolk, Mummy, Vampire	1.0
Centaur, Demigod, Draconian, Ghoul, Hill Orc, Minotaur	1.1
Deep Dwarf, Naga	1.2
Ogre, Troll	1.3

And the HP bonuses for each background are:

Background	HP Bonus
Wizard	6
Conjurer, Enchanter, Fire Elementalist, Ice Elementalist, Air Elementalist, Earth Elementalist, Summoner, Venom Mage, Necromancer	8
Wanderer	9
Arcane Marksman, Stalker, Transmuter, Warper	10
Abyssal Knight, Chaos Knight, Death Knight, Healer, Hunter, Monk, Priest, Skald	11
Gladiator	12
Fighter, Berserker	13

Some spells can also change your maximum HP:

Spell	Modifier
Ice Form	1.2
Statue Form	1.3
Dragon Form	1.5

Finally, Berserk Rage will multiply your maximum HP by 1.5.

If at any time your character's current HP reaches 0 or lower, he dies and your game is over. You can avoid this by resting between battles, quaffing potions of heal wounds or curing, or using any of the more exotic healing methods available.

Be very careful if you ever see the message, "Ouch! That really hurt!" pop up, as it only occurs after you've lost 50% or more of your max HP in a single attack.