Magnetic therapy is an alternative medical practice that uses static (i.e. unmoving) magnets to alleviate pain and other health concerns. So-called therapeutic magnets are typically integrated into bracelets, rings, or shoe inserts, though therapeutic magnetic mattresses and clothing are also on the market.

Many well-conducted studies over the past three decades have shown that static magnetic devices offer no more or no less benefit than sham devices devoid of a magnet. These studies suggest that static magnetic therapy devices may not work at all beyond having a placebo effect on those who wear them.

Despite a lack of scientific evidence to support claims that commercially available magnetic therapy devices work, wearable magnets remain extremely popular. Global sale of therapeutic magnets is estimated to be at least $1 billion a year, according to the BBC.

How it's supposed to work

Magnetic therapy dates back at least 2,000 years, according to a report by New York University's Langone Medical Center. Folk healers in Europe and Asia are believed to have used magnets to try to treat a variety of ailments. These healers may have believed that magnets could actually draw disease from the body.

Today, those who believe in the efficacy of magnetic therapy often cite the ability of static magnets to alter a person's bioenergetic fields, or biofields, which are "energy fields that purportedly surround and penetrate the human body," according to the American Congress of Obstetricians and Gynecologists. Practitioners of certain alternative medical techniques may refer to this alleged bioenergetic field as life force, chi or energy flow. Some believe that such fields can be manipulated — sometimes using magnets — to treat illness or injury, according to an article published in 1999 in the Scientific Review of Alternative Medicine.

Many companies that sell therapeutic magnets also claim that a small magnet inside of a bracelet or other device helps increase blood flow to the area of the body where the device is worn. This increased blood flow is then said to help tissues heal faster.

While this idea may sound plausible because blood contains iron and magnets attract iron, the iron in blood is bound to hemoglobin and is not ferromagnetic (that permanent kind of magnetism that keeps magnets on a refrigerator, for example). If blood was ferromagnetic, you would essentially blow up when undergoing an MRI scan, in which the magnets used are thousands of times more powerful than those incorporated into magnetic bracelets and the like, according to an article by Dr. Bruce Flamm, a clinical professor of obstetrics and gynecology at the University of California, Irvine.

Regardless, the therapeutic magnets sold to ease aches and pains have magnetic fields that are generally too weak to penetrate your skin. You can test this by observing the weak interaction between a magnetic shoe insert and a paperclip when separated by a sock. Human skin is about 3 millimeters deep, thicker than some socks.

The most commonly used therapeutic magnets measure 400 to 800 gauss (one of the units in which magnet strength is expressed). Also known as permanent magnets, the static magnets used in magnetic therapy devices come in two different polarity arrangements, according to the Langone Medical Center report. The magnets are either unipolar, which means they have north on one side and south on the other, or they are alternating-pole, which means they are made from a sheet of magnetic material with north and south magnets arranged in an alternating pattern.

What the studies say

Scientific studies on human subjects have failed to show the efficacy of using magnets to treat pain or joint and muscle stiffness. One of the largest studies was published in 2007 in the Canadian Medical Association Journal — a systematic review of numerous previous studies on static magnets.

While some smaller studies in this review reported therapeutic value, larger studies did not. The researchers concluded: "The evidence does not support the use of static magnets for pain relief, and therefore magnets cannot be recommended as an effective treatment."

One positive result often cited by magnetic therapy advocates is a 1997 study from Baylor College of Medicine, titled "Response of pain to static magnetic fields in postpolio patients: a double-blind pilot study."

This study, led by Carlos Vallbona, reported "significant and prompt relief of pain in postpolio subjects" through the use of a 300-500 gauss magnet (about 10 times stronger than a refrigerator magnet) for 45 minutes on the affected area of 50 patients in pain.

But the Baylor study was both small and somewhat controversial, according to James Livingston, a retired MIT lecturer and former physicist with General Electric. Both doctors who conducted the study reported that they had used magnets to relieve their own knee pain prior to the study. This raises some doubts about the researchers' objectivity, Livingston said.

Vallbona and his fellow researcher never duplicated their positive results in a larger study and, in fact, never published again on the topic.

In 2006, UC Irvine's Flamm took a closer look at the science behind therapeutic magnets in an article that he published with Leonard Finegold, a professor of physics at Drexel University. For their article, published in the British Medical Journal, the authors reviewed the scientific literature on the efficacy of commercially available therapeutic magnets to treat a variety of ailments. They found no evidence that such magnets actually work.

"As far as static field magnets, there is definitely no evidence that they work," Finegold told Live Science.

Finegold's assertion is in keeping with the position of the National Center for Complementary and Integrative Health (NCCIH) on magnet therapy. The NCCIH's website states, "scientific evidence does not support the use of magnets for pain relief." The organization also states that no such evidence exists to support the use of magnets in the treatment of conditions such as fibromyalgia.

Additional reporting by Christopher Wanjek, Live Science Contributor

Follow Elizabeth Palermo @techEpalermo. Follow Live Science @livescience, Facebook & Google+.

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