Immunity to electromagnetism
Jack was seemingly made ageless when he became Jacob's replacement as the Protector of the Island. He passed on the role to Hurley. Just like Desmond, Jack was shown to survive the high amount of electromagnetic energy released by the source, although he died (this because the Man in Black stabbed him with a knife), he was alive after he put the cork on the source of the light. He had enough strength to make it to the bamboo forest, but shortly after, died. Note: there were several dead bodies in the cave, demonstrating no one other than Desmond and Jack have survived the electromagnetic energy generated by the source.