Google has cracked down on pervasive, predatory ads promoting sketchy medical treatments — a move that could affect many of the hundreds of stem cell treatments advertised online.

At the end of October, the internet giant stopped accepting ads for “unproven or experimental medical techniques,” according to a statement from the company. Google is taking this step after seeing a rise in “bad actors” offering “deceptive” and “untested” treatments, the company said.

Stem cells came up this week during the senate confirmation hearing for the next head of the Food and Drug Administration on Wednesday.

"FDA has taken enforcement action, which it should, against stem cell clinics and manufacturers that might be misleading people," Sen. Lamar Alexander (R-Tenn.) said. "On the other hand, we have diabetes advocates who say regenerative medicine may restore pancreas or put out of business a heart transplant surgeon by restoring a heart. Will you commit to taking seriously the promise of regenerative medicine and stem cell medicines?"

Dr. Stephen Hahn, President Trump's nominee to lead the agency, replied that he would "certainly commit to that."

The number of stem cell clinics in the U.S. doubled every year from 2009 to 2014, according to a report in the journal Regenerative Medicine.

Major renowned medical centers such as the Mayo Clinic are researching stem cell therapies for conditions including arthritis and heart problems.

But as stem cell clinics not affiliated with medical centers proliferate, so have serious concerns. In 2017, the New England Journal of Medicine reported that three women were virtually blinded from unproven "stem cell" treatments that actually involved having fat injected into their eyes.

That has brought increased scrutiny from the FDA, which in June won a court ruling allowing the agency to regulate treatments at the Florida clinic where the three women were harmed.

Stem cell products have only been approved for two uses by the agency: for blood cancers and certain immune disorders. That hasn’t stopped some providers from claiming their stem cell treatments can "cure" a wide range of conditions, from macular degeneration to multiple sclerosis — unapproved treatments that are not only not effective, but could pose serious health risks.

What are stem cells, and what can they do?

Stem cells are very young cells that can develop into specialized cells, such as blood cells, bone cells and brain cells. According to the FDA, stem cells “have the potential to replace, repair, restore and regenerate other cells, and could possibly be used to treat a number of medical conditions.”

The only stem cell-based products currently approved by the FDA consist of blood stem cells derived from umbilical cord blood. These products are usually used in patients with blood cancers, such as leukemia and immune disorders. For patients with blood cancers, for example, stem cells are used after chemotherapy to replenish the blood cells that were destroyed during the treatment.

Morsa Images / Getty Images

However, other uses are being studied. There are currently more than 650 active clinical trials for stem cell procedures, looking at a myriad of conditions including kidney failure and Crohn's disease.

But the purpose of a clinical trial is to determine if a treatment works or if it's safe.

“People should understand that they're trying something that could potentially have benefit,” Dr. Peter Marks, FDA director of biologics, said. “But we don't know that benefit is really there, which means that they should understand the risk.”

“We do our best to make sure people are safe when they're getting investigational products,” Marks said. When a product is in a clinical trial, the FDA can monitor it to make sure it’s safe, he added.

Staying safe when considering stem cells

For patients considering stem cell treatments, the FDA recommends asking a health care provider if the FDA has reviewed the treatment.

This also applies to stem cell treatments that use a person's own cells. “You may be told that because these are your cells, the FDA does not need to review or approve the treatment. That is not true,” according to the FDA website.

“The FDA has given that road map on how to do it responsibly,” said Dr. Shane Shapiro, medical director at the Mayo Clinic’s Regenerative Medicine Therapeutics Program in Jacksonville, Florida.

Shapiro also recommends going to a provider that has an expertise in the disease or injury that they are offering stem cell products to treat.

“I think it is important to point out when we see a patient at Mayo, they are still seeing someone with the expertise of a physician that is a specialist in the disease they need help with,” he said.

Follow NBC HEALTH on Twitter & Facebook.