Werewolves are able to siphon off pain of another living creature through touch. They absorb the pain, alleviate it, causing them some discomfort, but on a level out of scale with the amount of pain dissipating from the recipient.
It hurts the werewolf less than it hurts the person they're helping. On the negative side, if the werewolf takes too much pain away, the assorted bouts of pain could very well kill him.
In the natural world, in wolf packs, when a member of the pack is injured the other members will never abandon him. They regurgitate food into his mouth, they care for him, groom him in order to comfort and alleviate the injured member's pain. A werewolf's pain siphon appears significantly relevant to this phenomenon.
In Battlefield, Isaac seemed to feel pity and morsoe for a dying dog. Under Dr. Deaton's direction, Isaac was able to activate his pain siphon ability for the first time, to his heartfelt joy.
In Ouroboros, Liam Dunbar attempted to use his pain siphon for the first time on Hayden Romero, but failed. Later when he and Hayden share a sweet moment, they kiss, and Liam's pain siphon works then. This indicates werewolves can't just think about taking the pain for an individual to activate it, they have to have a degree of empathy for the individuals they're helping.
Alphas, however, can use the pain siphon to heal, although at great personal cost.