Have you ever taken a test and you needed to get a 90% to get an “A"? You might have felt OK about the test afterward, but you started to worry once you got home. Did you score high enough to get that “A"?
When you get back to school and your teacher passes out the graded exams, you close your eyes and wait for your paper. When you open your eyes, you see it there in the corner. An “A"! You got a 91%. Whew! That was close. You got your “A," but just barely…
Another student who sees your paper might say that you got that “A" by the skin of your teeth. What's he talking about? Teeth don't have skin, do they?
The phrase has ancient origins in verse 20 of chapter 19 of the Book of Job in the Bible. Describing the illness that has made him so sick that he barely has anything left of his body, Job says, “My bone clings to my skin and to my flesh, and I have escaped by the skin of my teeth."
Despite its old roots, it doesn't appear that the phrase became popular until the nineteenth century. Although it's a very common phrase today, it can be confusing for many kids the first time they hear it. After all, it's not like you have skin on your teeth like you have on the rest of your body.
The phrase takes its meaning from this very fact. If your teeth did have skin, it's so thin as to be imaginary! In other words, it's barely there!
Some clever kids who know a lot about teeth might mention that sometimes your teeth do have a sort of skin on them. Microscopic bacteria in your mouth can form a film called plaque on your teeth overnight. This microscopic film can't be seen, so it's barely there, too! Either way you look at it, “by the skin of your teeth" is a good way to get across the message that something barely happened.