Swimmer Michael Phelps is the most prominent athlete to appear with circular bruises over his body this week, raising eyebrows and questions.

Is he okay? Is he a closet hemophiliac? Is he—oh no—he’s not smoking pot again?

Olympians are now allowed a modest amount of THC in blood tests, so he might be. But that would only tangentially explain the bruises, which are self-inflicted, the result of a practice known as cupping.

The process involves small, glass cups that look like shot glasses with nipples being placed over his skin, and a practitioner then inducing a vacuum inside the cup by heating the air. That suction pulls his skin up into the cup, breaking capillaries and causing blood to pool and stagnate, creating a bruise. That’s why the process is also known as “fire cupping” and “sucking method.”

A not-recommended Google-image search will show you some horrendously purple injuries. Phelps’s are relatively minor. He and some other athletes undertake them because they believe this process helps muscles to heal more quickly by encouraging blood flow. A bruise is a blood clot, though, and clotted blood is definitionally not flowing.

So in terms of role-model behavior, cupping may be more deleterious than a grainy bong photo, because it invites people to distrust science.

What takes this self-injury-with-unclear-ends from psychopathology to hip trend is the fact of it being an “ancient Chinese therapy.” Those aren’t dismissive, skeptical quotations—people in China have indeed been doing it for centuries, as a therapeutic pursuit—just a restatement of the common buzz phrase that is integral to the appeal of the practice. Something about the oldness, and the non-Western-ness, gives it some enduring anti-establishment cred. And it’s always fraught to criticize a practice that’s so historically intwined with a particular culture so that the two become inseparable. Denying the efficacy of a health intervention is denying a part of someone’s identity.

But here I am. Because I also don’t like seeing people waste money when they don’t know they’re wasting money.

Beliefs about how cupping benefits a person are multitudinous, limited only by the imagination. And, in terms of scientific evidence, substantiated only by the imagination. Cupping has not been studied in large, controlled clinical trials. Part of that is because it would be difficult to have a control group. If you’ve been cupped, you know it. (Hence the meme “Quit cupping me, bro.” Ed: Not an actual meme.) Placebo effects can be strong, especially in domains as psychologically dependent as high-performance athletics.

Studies aren’t especially important to the practitioners who sell cupping, anyway, because the industry that profits from cupping in the United States—the enormous “alternative” medicine industry—defines itself as one that does not deal in evidence. A lack of evidence rather paradoxically makes some practices more appealing to those who are seeking answers outside of the health care system.

Things like cupping, cryotherapy, chelation, and IV nutrient therapy sell in this space not despite the fact that they aren’t proven to work, but because of it. These practices have much in common with the political ascent of Donald Trump, who is appealing to many because of his inexperience and lack of traditional leadership qualities and characteristics. Such reactionary appeal will persist in health as in politics, in the face of any contrary evidence, and despite the lack of a plausible mechanism.

With the most decorated Olympian in history serving as some paddle-footed, swimming billboard for cupping, I don’t expect anything I can say will stem the coming tide. And I also don’t want to feed the forbidden fruit appeal. So the bottom line might be this: If you have the disposable time and money, and cupping makes you feel good, and it’s not undertaken at the expense of any evidence-based health endeavors, and you don’t have any blood clotting disorders or any other medical contraindication, it’s probably not going to hurt you in any way other than the pain it causes.