Life
From Diablo Wiki
Life is the amount of health/hitpoints that a player character has. Each time a player is hit, their life goes down. When it reaches zero, the player dies. Life can be recovered with potions of healing, speaking to a healing NPC, or with the Life Stealing weapon modifier.
Life can be replenished by the use of Healing Potions and Rejuvenation Potions. Healing potions heal over time while Rejuvenation potions act instantly.
[edit] Healing NPCS
The amount of maximum life is affected by items with life bonuses, or Stat Points invested in Vitality
Life can also be increased permanently by use of certain elixirs prepared by talented alchemists like Alkor in Kurast. In Diablo II, it increased life permanently by 20.
Note that you cannot die from poison, because poison can only lower your hit points to 1. But your Hireling can die from poison.
