The use of heated glass cups placed on the skin causes the skin to tent into the cups as the cups cool, creating a vacuum.  Multiple cups are used, and may be wet or dry.  The technique was used as far back as 1550 BC by the Egyptians.  Modern cupping may use silicone, wood or glass or other substances and many have valves to release the cups.  This is part of the Traditional Chinese Medicine (TCM) system used to treat pain, inflammation, increase blood flow, enhance well-being, and as a type of massage. The technique is all the rage in today's alternative medicine treatments in the US.  There is some scientific proof cupping is effective. 

• J Back Musculoskelet Rehabil. 2017 Nov 6;30(6):1187-1195 A meta-analysis of randomized trials demonstrated significant effectiveness for the treatment of low back pain

• J Pain. 2009 Jun;10(6):601-8. Cupping of the trapezius for carpal tunnel syndrome led to significant reduction in pain (RCT)

• A systematic review of studies in 2011 (Evid Based Complement Alternat Med. 2011;2011:467014) it was found there were two randomized controlled trials showing some benefit in pain treatment and one that found no benefit. Overall, the quality of the available studies being conducted by those using cupping are so poor that no conclusions may be drawn about efficacy. 

Injuries from cupping, while rare, may be serious.

• Interv Neuroradiol. 2016 Dec;22(6):728-731 Cupping was associated with a vertebral artery rupture and large hematoma on the back of the neck

• Wounds. 2014 Jul;26(7):214-20.  Burn injuries from cupping in China are not uncommon, more often seen with wet vs. dry cupping

• J Dtsch Dermatol Ges. 2015 Apr;13(4):337-8  Cupping may cause permanent dermal scarring

• J Cutan Med Surg. 2015 May-Jun;19(3):320-2  Cupping may induce psoriasis in areas under the cups

• J Burn Care Res. 2011 Mar-Apr;32(2):e31  Burn injuries due to cupping

• J Altern Complement Med. 2009 Nov;15(11):1243-5.  Cupping may create severe blistering as well as bruising