If you watched the 2016 summer Olympics swimmers — especially super-star Michael Phelps — you could hardly avoid noticing what looked like great big hickeys on various spots on their bodies — like these:
But no, these aren't hickeys, they're the results of an ancient Chinese/Egyptian technique called cupping. A therapist puts special cups, which might be made of glass, bamboo, silicone or earthenware, on your skin to create a vacuum. The cups contain a flammable substance (e.g. alcohol, herbs or paper) which are set on fire: when the fire goes out, the cups are placed on the skin. As the air inside the cups cools, it contracts, setting up a vacuum which exerts a negative pressure on the skin. This will break small capillaries in the skin, causing the characteristic hickey-like appearance. In modern times, the vacuum may also be accomplished by attaching the cups to a real source of vacuum, such as a vacuum pump or syringe, as shown below.
And the purpose of this, you may ask? Well, theoretically it can help treat pain, deep scar tissue in muscles and connective tissue, muscle knots, and swelling. But there's no scientific evidence that the procedure can really do any of that. So we may have yet another placebo effect that leaves its traces on users.