Answer:
In we go, out we go. All around and in a row. Always, always steady flow. When we'll stop, you'll never known. In we go, out we go.
I can be short and sometimes hot. When displayed, I rarely impress.
When young, I am sweet in the sun. When middle-aged, I make you gay. When old, I am valued more than ever.
The strangest creature you'll ever find has two eyes in front and a hundred behind.
No matter how little or how much you use me, you change me every month.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?