Answer:
Hard to catch, easy to hold. Can't be seen, unless it's cold
He stands beside the road. In a purple cap at tattered green cloak. Those who touch him, curse him.
By Moon or by Sun, I shall be found. Yet I am undone, if there's no light around
Lovely and round, I shine with pale light, grown in the darkness, a lady's delight.
Though desert men once called me God, today men call me mad. For I wag my tail when I am angry. And growl when I am glad.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?