I was wondering if a person who has One For All will lose his One For All once he passes it on to someone else. All Might just gave one hair to Izuku so he might not have lost his power. But if someone completely passed on One For All would they lose their One For All?
Im not sure how much of the Anime/Manga you have watched or read but its very clear that All Might is losing/has lost his power after giving it to Izuku Midoriya. In the climatic battle against All for One in Season 3 its shown that the embers of One for All that All Might had left died out and he used the last of his power to defeat him.