Health Bar
51%-100% is Healthy: Survivors have a green silhouette.
16%-50% is Hurt: Survivors have a yellow silhouette and walk slower.
1%-15% is Near Death: Survivors have a red silhouette and walk
very slowly.
Med Kits
It takes 5-6 seconds to use the first aid kit to heal yourself or another Survivor, during which time you cannot defend yourself in any way. (If you are being healed by another player, you may shoot, but you can't reload.) Instead of restoring a set amount of health, first aid kits will only restore 80% of the damage the Survivor has taken. For example, if a Survivor has taken 70% damage, using a first aid kit will add 56% (80% of 70) to the Survivor's health, bringing the Survivor to 86% health. This healing is not based on any temporary health a Survivor might have after taking pain pills, and will remove any extra health gained by them. Survivors healing after an incapacitation work on the same rules, and thus, always receive 80 health points. Please note that first aid kits can never bring a Survivor back to 100% health. You can also melee with your first aid kit, but you could accidentally start to heal someone in the fray. Usually found in safe rooms and sparingly through levels.
Defibrillator
This item is symbolized by a lightning bolt. It can be used to revive dead teammates and can only be used once. For balancing purposes, the player can not carry a defibrillator and health pack at the same time. To use the defibrillator, players must walk up to a corpse, which will acquire a faint red glow, and use it like a Med Kit. A charging meter, which takes 5 seconds to complete, is shown. Then, there is a short burst of electricity and the teammate has been successfully revived. He/she comes back at 50 health (which is permanent health that doesn't drop like temporary health gained when being revived after being incapacitated) and can pick up all dropped items before continuing. There will be a message on the left side of the screen informing everyone who brought whom back to life.
Pain Pills
Unlike the First aid kit, pills will only give the user 50 temporary points of health when taken. Pills can be given to teammates by pressing the melee button. When not facing a teammate, pressing the melee button will allow you to use your melee attack against enemies. Since the health from Pain Pills is only temporary, it will slowly decrease over time, dropping one point every few seconds until all the temporary health is gone. The pills you take will restore your movement speed and stop you from limping for as long as your total health is above (and including) 40%. Keep in mind if when you take damage when both permanent health and temporary health exist, permanent health will be taken first. If while pain pills are active your actual health (read: permanent) drops below zero, your temporary health will continue dropping until it reaches 1%, where it will stay until you heal, take some more, etc. A great way to make it through a tough area, but not a substitute for good health!
Adrenaline injector/Syringe
This uses the pain pills' slot and give you 25 temporary health plus they make you immune to melee fatigue and the horde's slowing melee attacks, as well as increase your movement speed a great deal for a short period of time. The health added by the injector appears to drop slower than the health from pills. Adrenaline injector is always seen in the Crescendo event in "The Park". Injecting oneself appears to give one a tunnel vision effect. This item could become valuable at the end of a Finale where Survivors are trying to get on the Rescue Vehicle but are constantly being slowed down by the horde. Similarly like the Pain Pills, Adrenaline Injectors can be given to teammates using the melee button. Using the Adrenaline causes any sounds in the game to become Mono. This means that you can't really determine where someone/something is via sound.
Note: Adrenaline no longer causes the users health to go above 99hp as it did in early access previews.
Incapacitation/Black & White
When your health drops to zero, you'll be incapacitated, or "incapped", until a teammate revives you. While incapped, you will have a "bleed out" health bar that will slowly count down. If no teammates come to revive you within that time frame, you will die. If you are revived, you'll be given a temporary health boost of 30 that will count down to 1 over time. If you are incapped again without receiving first aid, upon being revived you'll be "black and white," meaning that another incapacitation will result in your death unless you are healed with a med kit. Note that some modes forgo the Incapacitation stage resulting in immediate death.