The Rio Olympics is shining a light on the ancient Chinese medical practice called cupping, with athletes including the best swimmer in history, Michael Phelps, showing up for events with telltale round reddish spots on his arms. What is this practice? Does it hurt? Does it work? Should you try it on yourself?

To explore these questions, we spoke with one of the pioneers of traditional Chinese medicine in the US—Jeffrey Zimmerman, a doctor of oriental medicine, licensed acupuncturist, martial artist and qigong master, who practices in Westport, Connecticut.

Here are his answers to our questions…

Bottom Line: What is this cupping that the Olympic athletes are using?

Dr. Zimmerman: It’s one of the tools in traditional Chinese medicine.

American and other Olympic athletes saw Chinese swimmers use this in the Beijing Olympics in 2008—and now they’re doing it. A special small glass cup is used. Typically, a cotton swab is set on fire inside the cup and then allowed to go out, at which point the cup is quickly placed over the skin. As the heat dissipates, it creates a vacuum, pulling the skin up away from the muscle and lifting the fascia, a web of tissue that supports the muscle. These days, some cups come with a vacuum pump instead, so no fire or heat is used.

What does cupping do?

Dr. Zimmerman: In purely Western terms, it gently pulls up on the muscles, bringing blood flow to an area that may tend to be sore or inflamed—such as certain parts of a swimmer’s shoulders and arms. In traditional Chinese medicine terms, it promotes the free flow of chi (vital energy) in the blood in those areas.

What are those big red marks that cupping leaves? Do they hurt?

Dr. Zimmerman: They are caused by the tiny capillaries bursting under the skin. The procedure does not hurt before or afterward, and the red marks go away in a few days.

What are the supposed benefits?

Dr. Zimmerman: By releasing blood flow, cupping reduces swelling, reduces pain and accelerates healing. It’s good for swelling and pain caused by intense exercise as well as for sprains. In Chinese medicine terms, these are conditions in which the blood has become stagnant.

Is there evidence that it works?

Dr. Zimmerman: There haven’t been many large studies—I hope we can do more research on efficacy. What we have instead is what I call experience-based medicine. A form of cupping has been used not only in China but also in ancient Egypt, and, a fellow acupuncturist told me, in Ireland. It’s been used by martial artists for centuries. I don’t think Michael Phelps would go around looking like he was attacked by an octopus unless he were getting benefits. While not every traditional medical practice is trustworthy, this is an external technique that can be judged by its efficacy immediately—by reduced swelling, for example.

 Could the benefits be merely psychological?

Dr. Zimmerman: I doubt it. You see that it reduces swelling immediately, and it reduces pain quite quickly. If there is any psychological or placebo effect, I think that would just be an additional benefit.

 How does dry cupping differ from “wet” cupping?

Dr. Zimmerman: What the Olympic athletes appear to be doing is what is called “dry” cupping, in which the cup is stationary so it is just placed on an area and left there until it is removed. In “wet” cupping, a thin layer of oil, often an essential oil, is placed on the body so that a practitioner can apply the cup, then move it around easily to different spots—without losing the vacuum. For example, if you have back pain, your acupuncturist might place cups on both sides of the spine and move them up and down. As you are sliding them up and down, you can look at the effects. An experienced practitioner will be able to see spots where the skin takes a longer time to become pink, and that’s likely where the pain is coming from. Wet cupping takes more time and focus on the part of the practitioner, causing him/her to be more mindful of the process. It’s an art. If one particular area needs cupping, then dry cupping is appropriate, but if the blood and qi need to be moved over an area, then wet cupping is the preferred method. The knowledge and skill of the practitioner is the most important part of the treatment.

Don’t acupuncturists sometimes draw blood when they cup?

Dr. Zimmerman: Cupping can also be applied to an acupuncture point. I’ve seen this practiced in China. A patient had a bad case of shingles, which is caused by the herpes Zoster virus, all over his torso. A special needle was used to make a cut on the back of the knee—bladder 40 is the name of the spot—and then it was cupped to draw blood out. The next day, the patient was much improved. But this practice is not generally done in the US, and I don’t practice it.

Can cupping be useful for serious medical conditions?

Dr. Zimmerman: Yes, it has been studied for conditions ranging from herpes infection to acne to Bells’ palsy to asthma to knee pain, with good results. But if you have a serious medical condition, you need to have Western medicine as well. You need to be examined by all the great technology we have in Western medicine. Then you can also go to someone who is well-educated in traditional Chinese medicine who may use cupping along with other tools, including acupuncture, moxibustion, herbal medicine and nutrition. You don’t just go to someone who says, “I’ll cup that.”

What kind of health practitioner should one go to for cupping?

Dr. Zimmerman: I would start with a licensed acupuncturist. Ask if he/she is experienced with cupping.

Should you avoid cupping if you have certain medical conditions?

Dr. Zimmerman: If you are taking blood-thinning medication, this may be counter-indicated. Go to your doctor first and ask. That’s good advice if you are being treated for any condition—ask first if it’s safe.  It’s also important to have a conversation with the health-care practitioner so that you understand why he/she feels that cupping is good for you and your body.

Can people cup themselves or just ask a friend to do it on them?

Dr. Zimmerman: I’ve heard that there are kits that you can buy online. While it’s not particularly dangerous, I’m concerned about people who aren’t trained doing this. How would you know if you’re making it too tight against the skin? What if you leave it on too long? What if you fall asleep while the cup is on? You don’t know what kind of suction you’re creating—until you have a big bruise. I’m not aware of any permanent damage that it might cause, but it would take a much longer time for the bruise to heal. When you are being treated by a knowledgeable practitioner, his skill is there with you during the cupping.

Can a health practitioner who isn’t well-trained in traditional Chinese medicine do cupping safely?

Dr. Zimmerman: I can imagine chiropractors and physical therapists adapting cupping as a tool. I don’t have an objection to that for the treatment of sore muscles and certain injuries. But you want to find someone who has sincerely sought out training on cupping—not someone who took one weekend course. In every profession, there are good and bad practitioners.

Now that so many Americans are learning about cupping from the Olympics, what do you hope they take away about it?

Dr. Zimmerman: I hope people learn to take some of these ancient medical practices more seriously. I would hope that there is more research. For example, after many years, acupuncture has become accepted into mainstream Western medicine for both research and therapy. Traditional Chinese medicine has many tools, including Chinese medical massage, gua sha therapy (in which the skin is scraped to create mild bruising), that have benefits similar to those of cupping. We need to use the technology of Western science to show how these ancient techniques work. I hope that people say to themselves, If Michael Phelps is using this, maybe I should take a closer look.

To learn more about acupuncture, see Bottom Line’sGuide to Acupuncture: What It Does.

Note: To find a licensed acupuncturist, go to the website of the American Association of Acupuncture and Oriental Medicine (AAAOM). Use the “Find a Practitioner” search function to locate a licensed acupuncturist near you.