Earth FX’s half sheet plugs into a socket or connects to a rod in the ground. F. Martin Ramin/The Wall Street Journal, Styling by Anne Cardenas

The Verdict: There is little credible proof of health benefits, scientists say. Several studies show connecting subjects to an electrical ground changes bodily measurements, such as a marker of central-nervous system activity in infants. But the studies are “preliminary at best,” poorly designed and too small to be meaningful, says Steven Novella, a clinical neurologist at Yale University School of Medicine in New Haven, Conn., and executive editor of the blog Science-Based Medicine, which looks at controversies in science and medicine.

By living indoors and wearing shoes, “we have accidentally disconnected from the Earth,” says Clint Ober, founder and president of Earth FX Inc., Palm Springs, Calif. The company’s products, such as a fitted sheet for $180 and a $140 half sheet, are woven with conductive silver and are typically plugged into the ground, or third, socket, of wall outlets.

The Pluggz line of shoes, including $39 flip-flops and women’s shoes starting at $109, have circles in the sole infused with a carbon powder that conducts electrons from the Earth, says Sharon Whiteley, chief executive of Listen Brands Inc. in Tucson, Ariz.

John Cohn, a fellow of the Institute of Electrical and Electronics Engineers, a New York professional society, says it’s true that coming into contact with the Earth can cause the body to pick up electrons. Dr. Cohn and other scientists also say that plugging a conductive item, such as a sheet, into the third hole of a wall socket will have the same result, since it is connected to the ground.

But Dr. Cohn and others say the energy exchange isn’t an unusual event. The body gains and loses electrons all day routinely, says Chad Orzel, chairman of the department of physics and astronomy at Union College in Schenectady, N.Y., and nothing makes the Earth’s electrons special. “Every electron is identical to every other electron in the universe,” he says. Moreover, say Dr. Cohn and Dr. Orzel, any electrons picked up will remain mostly on the skin—making a positive health effect seem unlikely.

Advocates of earthing’s positive benefits point to a company-financed, eight-person study that found decreases in post-exercise muscle pain in subjects who spent evenings and nights grounded.

Grounding was tested by Penn State researchers in a study of about 20 infants hospitalized after birth in the intensive-care unit. The study was presented as a poster presentation at a meeting of the Pediatric Academic Societies earlier this month in Vancouver, British Columbia. When the babies were grounded using an electrode on their legs plugged into a grounding socket, scientists measured improved activity of the vagal nerve, which is involved in the body’s relaxation response.

The improved vagal-nerve activity—which a previous study linked to reduced risk of an inflammatory bowel disease common to newborns—disappeared when the electrode was removed, says Charles Palmer, a study co-investigator with no financial connection to Earth FX. The result is “very intriguing” but needs to be replicated by other scientists, says Dr. Palmer, chief of newborn medicine at Penn State Hershey Children’s Hospital in Hershey, Pa.

—Email aches@wsj.com