Suction cups are cups that have a small pump attached. They are placed on a person’s skin, and then the air inside them is pumped out, creating a vacuum which pulls on the skin. They are most commonly made of durable glass, but there are also metal and plastic versions.
Suction cups are used in alternative medicine mostly on muscles, to pull impurities from the skin. In BDSM scenes, the cups are used on other body parts, including the breasts, nipples, and penis. The result is painful, but the amount of pain can be controlled by the amount of suction: the more air removed, the more pain is caused.
The cups will usually leave a mark on the skin similar to a hickey. There are also safety risks involved when using suction cups: blood vessels might rupture, and prolonged use can cause headaches, dizziness, and nausea.