As a dripping-wet Michael Phelps celebrated his 19th Olympic gold medal on Sunday evening, viewers at home might have found themselves squinting at his shoulders and wondering about the large purple-red polka dots on his skin: What are those purple spots all over @MichaelPhelps? @USASwimming? Congrats on Gold #TeamUSA — Courtney Norris (@courtneyknorris) August 8, 2016 Those spots come from a traditional Chinese medicine treatment called "cupping," when large hot suction cups are left on the skin for several minutes, resulting in hickey-like marks.