In Dark Souls, one humanity point is needed to reverse Hollowing at a bonfire.
The player must first possess at least one usable humanity in the counter at the top-left of the screen. At a bonfire, the “Reverse Hollowing” command consumes one humanity and restores the character’s human form. Humanity held as an inventory item is not automatically the same as the active counter until it is used.
Human form enables several important systems, including summoning other players and being invaded. It can also allow certain scripted invasions or cooperative signs to appear. Reversing Hollowing does not itself restore health, and it does not spend souls.
The mechanic is often confused with kindling. Kindling also requires humanity, but it is a separate bonfire action that increases the number of Estus Flask charges available there. Further kindling requires the Rite of Kindling, while reversing Hollowing always costs one humanity.