Answer:
You use it between your head and your toes, the more it works the thinner it grows. What is it?
If you happen to wake up at dawn, you'll probably find this covering the lawn.
What is at the end of a rainbow?
Hearing something unexpected or touching a live wire can have this effect.
A king wears one on his head.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?