Answer:
When I live I cry, If you don't kill me I'll die.
You can see nothing else, When you look in my face, I will look you in the eye, And I will never lie.
You use it between your head and your toes, the more it works the thinner it grows.
My first half is normally made of stone, my second is crazy, and I taste sweet when complete.
I'm very tempting, so its said, I have a shiny coat of red, and my flesh is white beneath. I smell so sweet, taste good to eat, and help to guard your teeth.
What can you lose that will cause other people to lose theirs too?