Toughness is the measure of health points for all explorers, companions, and enemies. These points are widely variable between different characters, but is generally the same for all characters of the same type. Companions' toughness can be increased by promoting them.
Toughness is largely affected by combat. An enemy is killed when their toughness drops to 0. Any explorer or companion who's Toughness drops to 0 "passes out", and any of their applicable dice are removed from the player's rolls until combat ends. If combat ends successfully, any characters that passed out stay with the party. However, if the player is forced to flee from combat, any companions at 0 Toughness will be left behind and lost. An explorer can still flee while at 0 Toughness, as long as at least one of their humanoid companions (or animal companions, in the case of using explorer Alexandra David-Neel) has positive health points.
After combat, players and companions with lost toughness slowly regenerate their health points over time, unless they are Injured or have an Infected Wound . These ailments prevent the afflicted character from regenerating health until they have been treated with either a red mushroom or first aid kit .
Toughness can also be affected by negative events when a player rests at low Sanity, or travels through hazardous terrain such as fire or fumarole gas. Almost all physical ailments acquired in these ways negatively affect Toughness.