LITTLE OVERSIGHT

Stem cells can divide and renew themselves over long periods, and some can grow into any kind of cell in the body. Eventually, researchers say, stem cells could be used to treat many diseases, including macular degeneration, diabetes and Parkinson’s.

But those therapies are still being developed; the only FDA-approved stem-cell treatment is for blood disorders like leukemia. Many leading researchers compare the products being sold now to snake oil, saying there is little oversight, little scientific rationale for the procedures and little proof they have any effect.

Meanwhile, doctors have found evidence of harm: Several people have gone blind after receiving stem-cell treatments, according to reports in the New England Journal of Medicine and elsewhere. And two people died shortly after being injected with stem cell treatments in Florida, most recently in 2012.

The for-profit stem cell business is nonetheless booming. After cropping up overseas in countries such as Thailand and China, the industry has flourished in the United States — without much resistance, until recently, from the FDA or other federal regulators. Academic experts have identified at least 716 U.S. stem cell clinics and say the true number probably exceeds 1,000.

Many clinics use patients’ own tissue — belly fat, blood or bone marrow — to fashion treatments. More recently, practitioners have begun offering treatments manufactured from birth-related products, including discarded placentas, amniotic tissue, umbilical cords and cord blood.