Why Is The Outer 1 Inch Of All Sterile Field Considered Contaminated?

Why Is The Outer 1 Inch Of All Sterile Field Considered Contaminated? Why is the outer 1 inch of all sterile field considered contaminated? It is considered contaminated because microorganisms from a non-sterile surface can go through a wet cloth or paper by cappillary action. The one inch border at the edge of the sterile