Skill upgrades are a feature in The Last of Us.
There are distinct areas of skill upgradability including maximum health, listen mode distance, crafting speed, healing speed, weapon sway, and shiv mastery.
Each skill has a limit on the number of times it can upgraded. For instance, crafting speed and healing speed may be upgraded three times each, but maximum health may only be upgraded two times. These upgrades use supplements found or earned around the game world.