While competing for gold medals in Brazil, some athletes have been sporting ring-shaped bruises.

This isn’t a nod to the Olympic rings. These are the signature marks of cupping, an alternative therapeutic practice that involves suction and sometimes smoke.

The most decorated Olympian of all time, swimmer Michael Phelps, bore the circular bruises on his arms, shoulders, and legs this week.

Others, including fellow U.S. swimmer Natalie Coughlin and gymnast Alex Naddour, have been competing in their events with bruises that look like they stumbled through the table tennis matches.

The purpose, proponents of the therapy say, is to increase blood flow and nutrient supply to the muscles.

Dr. Jennifer Solomon, a physiatrist at Hospital for Special Surgery in New York, said cupping appears to be this year’s Olympic fad, just like Kinesio taping — a method said to support the body’s healing process — was in London four years ago.

“It’s just one of those things,” Solomon told Healthline. “Lots of my athletes use it and love it. Others don’t. Everyone responds differently.”

Before Olympic gold medalists and those vying for the title, celebrities like Justin Bieber, Jennifer Aniston, Lena Dunham, or Victoria Beckham have been seen with cupping marks.

While it’s relatively new to Olympians and Hollywood types, cupping therapy’s roots extend deeply into Eastern medicine.

Whether the therapy gives athletes a competitive advantage, or whether it’s in their heads is up for debate.

“There’s always a placebo effect,” Solomon said. “It’s strong.”

Cupping therapy raised some controversy earlier this year when Sonny Bill Williams, a New Zealand rugby player and boxer, posted photos of himself undergoing a somewhat bloody variation of the therapy.

This version is known as “hijama,” or wet cupping. “Hijama” means “drawing out” in Arabic. Some people undergo this therapy as a means of “detoxifying” the blood. The practice involves drawing blood out of a small incision using suction from one of these cups. Other methods of cupping do not involve cuts.

Wet cupping was endorsed by the prophet Muhammad. But the practice — wet or not — traces back to ancient Egyptian, Greek, and Chinese medical texts. It’s used as a form of detox therapy or deep tissue therapy, to refresh veins and arteries, and to treat pain.

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How cupping works

Cupping’s trademark bruises usually appear on people’s backs or torsos, and they follow the body’s “meridians,” or channels where “life energy” or “Qi” flows.

Glass cups are commonly used in most types of cupping therapies, but silicone cups are becoming more popular because they cause less bruising, and are often preferred for areas with sensitive skin, such as the face.

Historically, cups could also be made from bamboo, horns, or pots.

There are many variations of cupping, although there are three main varieties that use either glass or plastic cups.

1. Wet cupping

Wet cupping is called that because of the blood that is drawn from a person’s skin. Another name for it is Chinese bloodletting.

Cups are applied and then removed after a few minutes. Small incisions are then made and cups applied again, drawing blood into the cup.

The purpose is to remove “stagnant” blood from the body.

2. Dry cupping

Unlike wet cupping, dry cupping doesn’t involve an incision, so there shouldn’t be any blood leaving the body.

The cups — which range from one to three inches in diameter — are applied to the skin, and then suction is applied.

Mechanical and motor-driven suction pumps are becoming increasingly common as the practice expands in popularity.

3. Fire cupping

Fire cupping is when a cotton ball is soaked in isopropyl alcohol, lit on fire, and then quickly dipped into an empty cup. The flaming ball is then removed and the cup applied to the skin.

The practitioner may also coat the inside of the cup with alcohol, light it, and apply it to the skin.

The fire removes the oxygen from the cup, which creates the suction.

Practitioners may also apply oil to a person’s skin before the cups are applied, as it helps create a better seal.

This also allows the practitioner to move the cups over a person’s skin, which makes it a form of deep tissue massage.

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How effective is cupping?

Recent reviews of existing research on cupping therapy’s effectiveness found that most evidence supports cupping therapy’s potential benefits for pain management as well as helping people with persistent coughs, back problems, and conditions such as shingles.

However, even these researchers have advocated for more study.

Additionally, researchers have cautioned against some of cupping’s more adverse effects, especially for wet cupping.

Because wet cupping therapy involves making cuts into the skin, there is always the risk of infection, as well as swelling, bruising, and potentially scarring.

In California, wet cupping and other forms of bloodletting are illegal.

Even bloodless cupping has the potential to cause problems, such as keloids, panniculitis, damage to surface arteries and veins, and more.

And with fire cupping, there is also the possibility of suffering a burn injury.

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A need for standardization

There are no guidelines for cupping in the United States, and most practitioners come into the practice via massage or other alternative medicine practice.

With no centralized body overseeing it, courses that teach cupping and the people who perform it in the United States aren’t held to any standards or subject to any specific regulations.

In the United Kingdom, however, the British Cupping Society oversees and regulates the practice.

Recently, researchers have advocated for standardization, and once again pointed to the “poor clinical evidence” that it is beneficial.

As with most alternative therapies, there is little clinical supporting evidence that cupping therapy has major, lasting benefits.

There’s also a lot of debate surrounding its safety.

People with certain medical conditions, such as psoriasis, high blood pressure, or diabetes, should avoid cupping therapy, experts say, or any unsupervised practices that involve blood circulation or breaking of the skin.