A study finds that at least 351 U.S. companies with 570 clinics across the country are marketing stem cell treatments that are unapproved. These therapies range from simple health issues such as aging skin to more complex conditions including spinal cord injuries.

The online research discovered these "stem cell clinics" appear to be clustered in several states that include Florida, New York, California, Arizona, Colorado and Texas. However, they found much more scattered in various states.

In most cases, the clinics sell the unapproved stem cell treatments for people suffering from orthopedic conditions including injured tendon and ligaments, as well as arthritis. Medical experts warned that the science behind stem cell therapies for orthopedic problems is still "experimental."

Some clinics also market stem cell therapies, regardless of the lack of supporting evidence, for more serious health issues, including Parkinson's disease, multiple sclerosis and chronic lung cancer.

"In almost every state now, people can go locally to get stem cell 'treatments.' That's different from what we typically think about when we think of stem cell tourism," said study author and stem cell scientist Paul Knoepfler from the University of California at Davis School of Medicine.

The authors conducted an extensive online research on U.S. companies that are engaged in marketing stem cell treatments directly to consumers. They found 113 of such clinics in California, 104 in Florida and 71 in Texas. They found several "hot spots," including San Antonio, New York and Beverly Hills.

Data showed that practically two-thirds of the U.S. companies are offering unapproved procedures wherein the stem cells are procured from the patient's own fat. Nearly half of the clinics are offering treatments using bone marrow-based stem cell procedures.

The study authors did not accuse the clinics of illegal operations, however, they called for federal officials to step in and address the oversight. Co-author Leigh Turner, an associate professor at the University of Minnesota's Center for Bioethics, said they are worried that the unapproved stem cell treatments can cause "serious harm" to the patients.

Stem cells are primitive cells that can be persuaded into becoming nearly almost any type of cell. This suggests that therapies based on stem cells can help address many medical problems. Unfortunately, these cells also carry huge risks. They can develop into tumors and travel to other parts of the body.

"There is an obvious need for the FDA, FTC (Federal Trade Commission), state medical boards and other regulatory bodies to play a more effective role in regulating the marketplace for stem cell interventions," added Turner.

The research was published in the Cell Stem Cell journal on June 30.