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reality check

American Michael Phelps is seen with red cupping marks on his shoulder as he competes in the 200m butterfly at Rio Olympics.Dominic Ebenbichler/Reuters

If you've been tuning into the Rio Olympics, chances are you've noticed some of the athletes sporting circular red welts on their skin. They aren't the result of some bizarre Olympic Village hazing ritual. Rather, they are the result of an ancient – and controversial – treatment known as cupping.

So what is cupping – and does it provide an athletic edge?

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According to practitioners, cupping involves placing a cup on the surface of the skin and using heat or a vacuum to suction out the air, which causes the skin to redden. Some people undergo "wet" cupping, which involves pricking or slicing into the skin. The resulting blood flow is supposed to help eliminate so-called toxins. Proponents say cupping can promote healing and provide pain relief.

Although it has been around for centuries, practiced in ancient Egypt, China and the Middle East, cupping has recently resurfaced as a popular treatment for celebrities and athletes alike. Lena Dunham, Jennifer Aniston, Justin Bieber and Gwyneth Paltrow have all been photographed, or uploaded photos of themselves, sporting the telltale circular red marks after a cupping session in recent years. And over the weekend, several Olympic athletes, including U.S. swimming star Michael Phelps, also showed up with red welts on their bodies.

The evidence

While fans of cupping are quick to sing its praises, the evidence backing the effectiveness of cupping is much less clear. Like many other forms of so-called "alternative therapy," there are few high-quality scientific studies to demonstrate how well cupping works.

But one meta-analysis published in the journal PLoS One in 2012 provides some clues. In the study, researchers combed through scientific databases to find the most rigorous studies on cupping. They identified 135 clinical trials and analyzed them in order to summarize their findings. They found that cupping was most often used to help with the treatment of shingles, facial paralysis, cough and shortness of breath, acne, herniated disc and neck arthritis.

The researchers determined that for some conditions, cupping appears to have some benefit. But there's a huge caveat associated with the finding. According to the study authors, about 85 per cent of them had a high risk of bias, meaning the results may be skewed and should be taken with a large grain of salt.

One of the biggest problems was the fact the studies weren't properly blinded. In other words, study participants knew they were receiving a treatment that was supposed to provide symptom relief, which means they may be more likely to report positive effects after the cupping session. Although it's difficult to provide a placebo treatment, the study authors note that it is possible and that better research needs to be done before anyone can conclude that cupping works.

Reality check

Anecdotal evidence and the influence of celebrities or star athletes may convince people that cupping works. But the absence of rigorous evidence is a major red flag. In addition to the risk of redness, bruising or even infection (in the case of wet cupping), this type of therapy also poses a risk because it may steer people away from evidence-based therapies that can actually cure or treat their health problems.

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