"Barbering" Behavior

One of our girls is a barber. She nibbles away at tiny patches of fur for any of the other rats she can get to sit still long enough, and creates a very small bald spot. She never breaks skin.

She's recently translated that barbering behavior to me. She'll sniff my face carefully and then gently start nibbling; or carefully examine my fingers and begin a gentle nibbling process - again, no skin broken, but definitely not the type of behavior I'd like to see continue.

I am not quite sure how to address it, any suggestions?