Cupping involves placing cups made of glass, or silicone on the skin and creating a vacuum by suctioning out the air. The suction creates a negative pressure on the skin, which is believed to help improve blood flow and relieve muscle tension. During a cupping session, the cups may be left in place for several minutes or moved around the skin in a gliding motion. The suction may leave temporary marks but these are usually painless and fade within a few days.