My work is based on give and take,
I can make a difference by a hand shake,
The older I get the smaller I grow,
And my best friend is my worst foe.
What am I?
Give and take - give foam and take away dirt
By a hand shake - as you use me when rubbing your hands
The older I get the smaller I grow - since I dissolve
My best friend is my worst foe - Water which helps me do my work but at the same time dissolves me.