This is known as cupping, and is a great way to embrace your inner Polkaroo.
Thanks to the many sore athletes taking part in the Rio Olympics, cupping is having a bit of a moment right now. You've got swimmers and gymnasts with weird circular marks all over their torsos. The marks are some combination of erythema, petechiae, purpura, and ecchymosis. In other words, a bunch of blood ending up near the surface of the skin, the results of suction tearing open a bunch of tiny blood vessels.
|Just a run-of-the-mill cupping mark (Source)|
Setting aside whether or not cupping actually does anything useful (I'm betting on placebo), it turns out there are at least a couple of dangers associated with it.
First off, the traditional approach to cupping involves placing cotton doused in alcohol at the base of the cup, then lighting it to heat up the air inside. The cup is then cooled, resulting in suction as the pressure inside the cup is lowered. It might not surprise you to learn people occasionally are burned during a traditional cupping session. Nothing like hot glass on skin, eh? Modern cupping has eliminated this issue, as it involves the use of a hand pump to achieve suction.
One of the freakier ways of being hurt by cupping is having it done while flying. One case report I found told the story of a middle aged dude who ended up in emerge after being cupped while aboard his private airplane. Multiple blisters developed on the spots where the cups had been applied, each of which had to be drained with a needle. It's thought that a fairly rapid descent of the plane during the flight ended up increasing the suction inside the cups to the point at which skin begins to pop.
Problems can arise when cupping is carried out alongside acupuncture. In one reported case, an individual ended up with an abscess in their spinal cord. In other, the patient contracted herpes. It's clearly important to use clean equipment in order to avoid infection. Cupping and acupuncture can also cause serious issues for people with eczema. We're talking deep ulcers and intravenous antibiotics levels of serious.
In addition to injuries, cupping can mess with the efforts of forensic investigators. An article published last year in the Journal of Forensic and Legal Medicine warned that cupping-related skin damage could be misinterpreted during an autopsy as blunt trauma. There's also the possibility that a doctor might mistake cupping damage as evidence of a disease process and misdiagnose a patient.
Hon KL, Luk DC, Leong KF, Leung AK. 2013. Cupping therapy may be harmful for eczema: A PubMed search. Case Reports in Pediatrics 605829. [Full text]
Lin CW, Wang JT, Choy CS, Tung HH. 2009. Iatrogenic bullae following cupping therapy. Journal of Alternative and Complementary Medicine 15(11):1243-1245.