If you do something by the skin of your teeth, you only just succeed in doing it: “por los pelos”/”por un pelo”
Meaning ‘narrowly’ or ‘barely’, and referring usually to a narrow escape from disaster, the phrase comes from the Book of Job, in which Job is subjected to horrible trials by Satan, to be relieved finally by God. The precise phrase Job uses is slightly different:
‘My bone cleaveth to my skin and to my flesh, and I am escaped with the skin of my teeth’ (19:20).