Two inches below the skin what?

The bot that always replies to posts/comments on the sub about using tret around the eyes says that tret can travel 2” below the skin and I’ve always wondered if I’m reading it wrong? What does that even mean? Like if I apply tret to my forehead is it going into my brain? If I apply to the backs of my hands it will seep out my palms??

I know all topical medications can ultimately end up in the bloodstream… is that what that means??