Michael Phelps has single-handedly become the coolest dad and best meme at the Olympics, but when he competed in the 4×100-meter relay Sunday, he also caused a bit of a stir. When he took to the water to ultimately lead his team to the gold, many noticed weird round purple marks covering his right shoulder. What WERE those strange, perfectly symmetrical bruises? Had someone stuck suction cups all over him?

Well, sorta — the marks were the result of cupping, a form of alternative treatment therapy where cups, usually made of glass, are used to create a vacuum and lift the skin up in a localized area, sometimes resulting in the bruising seen on Phelps and other Olympics athletes (track and fielders are also big fans). It’s believed to get the blood moving and promote healing for a number of ailments, and it’s not just athletes that use it — it’s long been a trend in Hollywood for stars seeking natural treatments. Here are just some of the celebs who swear by cupping:

1. Gwyneth Paltrow: Gwyneth has been spotted sporting the telltale marks of cupping as early as 2004, sparking the trend you still see today in Hollywood. (Photo via Pascal Le Segretain/Getty)

2. Jennifer Aniston: When Jennifer was spotted with multiple cupping marks on her back on a red carpet in 2013, it was said that she was using it to help boost her fertility. While cupping can’t help women who have medical reasons for not being able to conceive, it’s said that the toxin removal and stress relief it provides might be beneficial. (Photo via Mike Windle/Getty)

3. Justin Bieber: Earlier this year, the Biebs was, ahem, spotted with the marks from what looked like an intensive cupping sesh. It’s possible he needed relief from working with weights, which is why the treatment was done on his abdomen and pecs. His astute fans noted that he looked like a pepperoni pizza.

4. Hailey Baldwin: Maybe hanging out with the Biebs resulted in Hailey’s experimentation with the procedure — she was spotted this past spring stepping out with a single circular mark, right between the boobs. Sure! (Photo via Dimitrios Kambouris/Getty)

5. Madonna: In the midst of her custody battle with ex Guy Richie and an 81-date world tour late last year, Madonna took some time out to get cupped. Out, damn toxins!

6. Lady Gaga: Gaga has been spotted with cupping’s round marks on her back — just another part of her intensive beauty regimen.

7. Victoria Beckham: Posh has been treating herself to the treatments since the early ‘aughts, often spotted with cupping circles up and down the length of her spine. (Photo via Peter Michael Dills/Getty)

8. Jessica Simpson: Jessica has raved about her experiences with the treatment as far back as 2010, saying that it has even caused her to have “intense visions.”

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Da Cure

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9. Lena Dunham: Lena outed herself as a fan of the practice two years ago, posting a pic of some fresh welts and a caption that read “Da cure.”

Have you tried or would you try cupping? Tweet us @BritandCo!

(Featured photo via Vittorio Zunino Celotto / Getty)