(CNN) Those dark red spots dotting Olympians' shoulders and backs are not cigar burns. They're not perfectly circular hickeys either.
Viewers watching the Olympics this weekend may have spotted the pepperoni-like bruises on athletes and wondered: What is that?
Olympians at Rio have taken to cupping -- an ancient therapy that have mostly been used in Middle Eastern and Asian countries, especially China.
The therapy consists of having round glass suction cups that are warmed, then placed on sore parts of the body. The placement of the glass cup creates a partial vacuum, which is believed to stimulate muscles and blood flow, while relieving pain.
Michael Phelps, US gymnast Alex Naddour and Belarus swimmer Pavel Sankovich have all posted pictures of their polka dotted limbs and backs.
Sankovich wrote earlier this summer on his Instagram account: "Cupping is a great recovery tool," with a photo of his thighs covered in suction cups. Former Olympic swimmer Natalie Coughlin has also previously posted pictures of herself going through a cupping therapy.
Phelps showed snippets of his cupping therapy on his Instagram as well as his Under Armour commercial.
It's not the first time cupping has made the rounds. Celebrities like Jennifer Aniston, Gwyneth Paltrow and Jessica Simpson have all been spotted with the marks in previous years.
Cupping is not new, it's ancient
Michael Phelps back has cupping marks, as he competes in the Final of the Men's 4 x 100m Freestyle Relay.
The practice of cupping has been mentioned in ancient Greek and Egyptian texts.
In traditional Chinese medicine, cupping dates back at least 2,000 years, according to a 2012 analysis published in the journal PLOS One. It is believed to restore the flow of "qi" -- the life force.
In recent years, cupping therapy has been used for people suffering all sorts of ailments including shingles, facial paralysis, cough and difficulty breathing and acne. But cupping is most commonly used to treat pain, according to the analysis.
One small study on cupping found that the cupping marks generally fade after two to four days.
What does the evidence say?
In previous studies, cupping has been used for treating cancer pain and lower back pain. In both of the randomized clinical trials, groups that received the cupping therapy reported more favorable effects in pain relief.
But this is just two trials with small sample sizes, so the researchers wrote in 2011 that it's hard to "draw firm conclusions" based on limited data, in a review published in Evidence-Based Complementary and Alternative Medicine.
Most published studies, however, focus on wet cupping, which is a form of medicinal bleeding. In this process, the skin is cut and the blood is pooled into the suction cup.
Based on social media photos, the athletes have opted for the non-bleeding therapy, which is known as dry cupping.
So far, the repeated effect of cupping therapy over time is not known, but it's generally believed to be safe, according to research published in 2012.
Perfectly circular bruises are adorning the bodies of Olympians in Rio this summer -- particularly among swimmers such as Michel Phelps (pictured) -- after the sudden
popularity of cupping, an ancient therapy practiced as far back at the 6th century. But this is one of many treatments used throughout history that aimed to control the flow of fluid within the body.
CNN spoke to Claudia Stein, professor of history at the University of Warwick, England, and Laurence Totelin, a historian of medicine at Cardiff University, Wales, to find out more about cupping and some of the more gruesome, but surprisingly commonplace, medical practices used to treat ailments throughout history.
Cupping therapy has been practiced from as early as the 6th century, according to Totelin, and is seeing a comeback today through the increased popularity of traditional medicine. "Globalization of medicine is attracting Western people to this holistic practice," says Stein.
The practice involves cups placed on specific regions of the body to create suction and encourage blood flow. Practitioners believe it promotes healing for a broad range of ailments in a similar way to the premise of bloodletting and leeching -- the goal being to balance levels of blood inside the body.
"Cupping was more common," says Totelin about the treatment which is still practiced today in Chinese medicine. In ancient times, however, its use was part of everyday life. "Cupping is one of the big things you do ... to be healthy," adds Stein. "[People would] place a cup to draw blood out of the body or to prevent getting sick."
Bloodletting is one of the oldest known medical practices and is thought to have begun with the ancient
Egyptians. This ancient practice involved the drawing -- or letting -- of blood from the body, which was believed to balance an individual's fluid levels.
Many ancient therapies were based on the belief that the human body consisted of four fluids -- or humors -- blood, phlegm, black bile and yellow bile. If their levels were thought to be out of sync, a range of unpleasant treatments were used to restore them.
The procedure came with strict rules and restrictions, with cuts only being made at specific points on the body. "It was a very complicated practice," says Stein.
"You would bloodlet if you have too much blood," says Totelin. The symptoms of excessive blood varied between individuals and genders, with females thought to be imbalanced if their menstrual cycles were disrupted, or delayed, and males if they were low on energy and sluggish, Totelin explains.
However, bloodletting was also practiced regularly at specific times of year in order to simply stay healthy -- such as in the springtime, when blood was thought to be thinner, according to Stein. "[People] used bloodletting in certain seasons to give a fresh start into their year," she explains.
A study in 2015 found that a thousand-year-old Anglo-Saxon potion (pictured) for eye infections
was effective in fighting the modern-day superbug MRSA.
Among its key ingredients was oxgall (bile from a cow's stomach) -- perhaps not the nicest thing to rub in your eye, but far more pleasant than many of the grisly treatments from medicine's murky past.
These blood-sucking worms were used in a similar way to bloodletting but provided a more localized way of extracting excess blood from the body. "You put leeches on the blood to draw bad fluid," says Stein.
The animals have evolved for optimal blood extraction from humans and release hirudin -- an anticoagulant -- during feedings to enhance blood flow.
Their use can be traced back to ancient Indian Ayurveda practices and leeches are still sometimes used in modern medicine to restore circulation after surgery.
Dating back before ancient Roman and Greek times, according to Totelin, holes were drilled into human skulls to relieve a range of ailments from migraines to head injuries.
The practice -- known as trepanation -- is considered by experts to be the oldest form of neurosurgery. Its original use was to relieve pressure, reduce swelling and also enhance overall bloodflow in the brain and improve well-being.
The premise behind the practice is still used by neurosurgeons today to reduce swelling and pressure in the brain before, or after, surgery.
For centuries, this poisonous chemical was taken in a range of forms -- pills, ointments, and inhalation. The one thing they all had in common was that they came with extensive, and long-lived, side effects including kidney failure, mouth ulcers and teeth loss. "We now know it was mercury poisoning," says Stein.
But the poison was considered an effective remedy, particularly against skin diseases. "Mercury was used for everything relating to skin diseases until the late 19th century," says Stein. It was also among the first treatments used
against syphilis.
Mercury was believed to help people sweat and salivate, in line with the belief of restoring fluid levels inside the body to treat ailments. One treatment involved rubbing patients with mercury ointment and locking them in a secluded, stuffy room to promote sweating. "[It was] seen as a sign of the body healing itself by getting fluids out," says Stein.
Many people died from mercury poisoning, rather than the disease it was meant to cure. This 19th-century illustration shows "part of the face destroyed by [syphilis] and the baneful effects of mercury."
From the 15th century onwards, people believed the body was made up of different elements which were needed in the right proportions. "If [they were] not, you used chemicals to put it in order," says Totelin. Those chemicals included lead, copper, silver and arsenic.
"Arsenic has always been a known poison," adds Stein, but its toxic properties did have some benefits. "It did kill bacteria but would not treat things long term," she says. In the 20th century arsenic was used in the first antibiotic treatment against syphilis, known as salvarsan, which was considered a magic bullet in the fight against the disease. It was a much needed alternative to pure mercury.
Couching is considered one of the earliest forms of cataract surgery dating back to the 6th century and possibly back to the ancient Egyptians, according to Totelin.
Cataracts cause a clouding of the lens inside the eye -- resulting in blurred vision. In couching, pointed objects were used to dislodge the lens within the eye and push the clouded section towards the back of the eye. "People were often blind at an early age," says Totelin, whose research has discovered couching to have been a long-standing practice.
The treatment continues to be used in some forms of traditional medicine today as well as in rural areas, but doctors warn against its use, instead advocating cataract surgery -- used in current Western medical practices.
Purging was a practice where poisonous plants were consumed to "rid the body of any superfluous liquids," according to Stein -- by inducing vomiting.
The aim was to empty the body of any of its contents which could be causing a person's ailments -- similar to the purging performed by cats and dogs.
"[There were] different plants you can give dependant on which area you live in," says Stein. A common plant consumed was hellebore -- also known then as the hell flower. Hellebore was also included in a range of ancient potions in ancient Greek and Japanese medicine. Its roots and stems were used to treat anything from melancholy and depression to coughs, epilepsy and dysentery.
This gallery was originally published in April 2016 and has been updated.
Olympians like fads, too
Every Olympics seems to have trendy items meant to help athletes, from high-tech swimsuits to the bright kinesio tape that made a scene in the London 2012 games. The tape appears to be back in Rio.
Unlike athletic tape, kinesio tape is thin and pliable, and meant to keep injured joints from bending to prevent further injury. The tape is used to prevent excessive protraction injuries, for example, shoulder problems from activities including playing tennis.
But the scientific evidence on kinesio tape is thin, according to a review published in the journal The Physician and Sportsmedicine. Studies showed that it improved pain and range of motion shortly after the injury, but the tape didn't make a difference in the long run.