Viewers watching the Rio Olympics likely spotted the bright-red circular bruises dotting the bodies of star athletes such as Michael Phelps and Alex Naddour in competitions during the past few weeks. The marks are evidence of the latest massage trend known as cupping, which claims to help rid the body of toxins, increase blood circulation and ease sore muscles. But a recent review of the latest medical research on the practice shows that this technique isn’t backed by science, The Dallas Morning News reports.  

Cupping is an ancient healing practice dating back to 1550 B.C. that involves lying face down on a massage table while a therapist attaches suction cups to the back, shoulders and limbs. Either heat or a pump is then used to suck the air out of these cups. That action creates a vacuum and pulls the skin into the vessels, which are then left on the body for five to 15 minutes. Practitioners of the technique say it’s like a massage that applies intense pressure to the tissues of the skin while bursting blood vessels to possibly promote circulation. Signature circular marks get left behind.

But here’s the thing: There’s no scientific evidence that cupping works. Most studies conducted on cupping thus far have been small, badly designed and incredibly biased. One larger study from 2012 that combined 135 reports of the practice found that cupping might be useful for treating acne and back pain but only when combined with pre-existing medications.

What’s more, many doctors said cupping could be incredibly dangerous, particularly when combined with bloodletting, a practice that involves slicing the skin with small cuts before suction cups are attached. If blades are not sterilized properly, patients can be put at risk of blood-borne diseases, such as hepatitis and HIV. Plus, reports documented that in rare cases cupping caused arteries to burst. In addition, bruising, skin irritation, burns and infections are common side effects of the unusual massage practice.

To learn more about alternative medical treatments that actually work, click here.