Health

"I need to find some Health!"

- Rochelle

Health is the hit point total that governs the survivability of the Survivors in Left 4 Dead. All Survivors begin with a total of 100 health at the start of every campaign, and when they complete a chapter their health will be saved for the next one. In Versus the Survivors will always begin a chapter at full health.

As the Survivors receive damage, their health decreases. When a Survivor's total health is 39 or less, they begin limping and their walking movement speed decreases from 220 to 150. If a Survivor has been revived from incapacitation but has not been healed by a First aid kit, then at the moment their health would decrease to zero (3.7 seconds after reaching 1 point of health), that Survivor's walking movement speed further decreases to 85. Crouching movement speed is not affected by any of these speed decreases.

Incapacitation
"Shit, I'm down!!"

- The Survivors

Once a Survivor's health has depleted to 0, they will be incapacitated and fall to the ground. They will only have access to a Pistol (two if they were dual-wielding before they were incapacitated) to defend themselves with, regardless of their primary weapon. Even if they were using a melee weapon, it will be changed into a standard Pistol. When incapacitated, a Survivor has 300 temporary health and must be helped up by teammates, or they will bleed out and die. Survivors also take reduced damage from some attacks when incapacitated but the Hunter will have increased damage.

Black/White Mode (Monochrome Vision)
When a Survivor has been incapacitated two times without being healed, their vision will turn black and white with a notable audio heartbeat to represent their current situation and item glows will increase and be red. If they fall for the third time without being healed with a First aid kit, they will be killed rather than incapacitated the next time their health reaches 0. Incapacitation can also happen when a Survivor hangs from a ledge - the same effects of reduced damage happen, but they do not count towards a black and white situation nor can you use your Pistols to defend yourself

Death
"This is going to hell in a hand basket real fast!!!"

- Bill

Upon death, the deceased Survivor will drop all of their weapons and items and turn into a ragdoll. In Left 4 Dead 2, however the Survivor dies with their arms spread apart and lying on the back. Dying does not mean that the player has been eliminated from the game, they simply need to wait one minute until transferred to the nearest rescue closet, and then have another Survivor rescue them. In Left 4 Dead 2 Survivors can also be revived by using a Defibrillator rather than a closet. When death occurs in Left 4 Dead 2, the Survivor will drop all items except their secondary weapon, whether it be Pistols or a melee weapon. This was most likely done so that if a player is revived through a Defibrillator, the player will have something to defend themselves with as they get up and will also have something in case their main weapon was taken. In Versus and Realism mode, the Defibrillator is the only option for Survivors to return during a level, as they cannot come back to life inside rescue closets. Otherwise they will have to wait until the Survivors are defeated, finished the chapter, or have restarted the round.

If all Survivors perish during the course of the game in Campaign, Realism, or Single Player, then the level they were on will reload with everyone back at the last safe room, with their health, weapons and items restored to what they had when they first entered that particular safe room during the current game. In Versus, Realism Versus, Scavenge, control of the Survivors and Infected is switched between the two teams. In Survival, the Survivors simply start a new game with everyone alive and at full health with First aid kits and Pain pills.

However, there are several other ways to lose the game related to death:
 * Being fully overcome by the Infected, leaving the group unable to play. However, if one (or more) Survivors are incapacitated and the last is dominated by a Smoker, Hunter, Jockey, or Charger, the incapacitated Survivors can still save the other Survivor with their Pistols/Magnums and it won't count as a loss, if saved before the last Survivor is incapacitated.
 * When a Jockey incapacitates a Survivor, he will leap off, allowing the Survivor to use their sidearm to help teammates (if within range). This often happen when the Jockey rides on a Survivor with low health, incapacitating the Survivor faster and not be ridden away.
 * The game is only over when every Survivor is either dead or incapacitated. There are still things that can kill the Special Infected or force them to release the Survivor in this situation, such as an explosion (a exploding Boomer, an item that is already been shot or on fire, a thrown Pipe bomb, or a grenade that is already in the air.), a "friendly" attack from a Tank, or fire that is already burning on the Special Infected.
 * Hanging from a ledge counts as incapacitation. So if three Survivors are hanging from a ledge and the fourth Survivor's health reaches zero, incapacitating them, the game will end.
 * Dying in Single Player mode, leaving the Survivor Bots to play alone.
 * Dying in Campaign, Realism, Versus, Realism Versus, Scavenge and Survival with all the other Survivor human-controlled players, leaving only Survivor Bots alive.
 * However, this will not be the case if "sb_all_bot_team" is set to 1. If there are no human players alive, the Survivor Bots will run through the map on their own. If they find a human player in a closet, or reach a safe room, the game will continue as normal with the human player leading the Survivor Bots again. Note that Bots struggle to trigger Crescendo Events and effectively run through a Rolling Crescendo on their own.

Healing
"Stop moving... I don't want to mess this up."

- Rochelle

Health can be restored in various ways:
 * Using a First aid kit removes all temporary health, and then restores 80% of the player's current missing health as permanent health.
 * In other words, if you have $$x$$ permanent health, using a first-aid kit grants you $$0.8(100-x)$$ additional health.
 * No matter how much your health is, when you heal your health will ALWAYS be either at 80 or above.
 * This can technically reduce your health total if you have enough temporary health. For example, if you have 50 permanent health and 50 temporary health, your total would be 100. If you then use a first-aid kit, then all of your temporary health is removed, and 40 of the 50 remaining points are healed, leaving you with a total of 90 permanent health, less than the original 100.
 * Using Pain pills grants 50 temporary health, which will slowly decrease to normal health as time passes.
 * Using an Adrenaline Shot grants 25 temporary health. The Adrenaline also makes you immune to melee fatigue and the horde's slowing melee attacks and allows the player to perform actions faster for a short period of time.
 * All forms of temporary health reduce at one point per 5 seconds.
 * When you take damage, your permanent health drains before your temporary health.
 * The Defibrillator can be used to bring a dead Survivor back to life. The Defibrillator will take the space of the First aid kit. It is a good idea for a Survivor with the least health to carry it:
 * 1) Because they have no health pack to drop
 * 2) Because if they die, another Survivor can pick it up and use it on them.
 * The defibrillator looks like a lightning bolt when you are carrying it. When you are revived with the defibrillator, you will be given 50 permanent health points, similar to how you'd be given 50 permanent health points after being taken out of a rescue closet.


 * Being revived from incapacitation grants the Survivor 1 permanent health and 29 temporary health (giving a total of 30). Incapacitating a teammate in order to do this is not recommended as a form of healing, of course.
 * Being rescued from a rescue closet grants the Survivor 50 permanent health and Tier 1 Weapons. The type of weapon depends on what the Survivor was carrying when they were killed. For instance, if the Survivor had an Assault Rifle, that Survivor will get a Submachine Gun when they are rescued. This will not occur if the survivors are overwhelmed and restart the chapter.