An apparatus for treating skin includes a chamber defined by a surface and a rim extending from the surface. A source of vacuum is capable of removing air from inside the chamber so that air outside the chamber flows into the chamber. Impedance of the air flowing between the rim of the chamber positioned adjacent the skin surface causes the pressure inside the chamber to decrease relative to ambient. A pressure sensor can determine when the pressure inside the chamber decreases to a threshold value. A controller can receive a signal from the pressure sensor when the threshold value is reached, which causes the rate of removal of the air from inside the chamber by the source of vacuum to be increased. The rim of the chamber forms a substantially fluid tight seal with the skin. The skin is drawn toward an inner surface of the chamber.