On the Internet, you can find advertisements for stem-cell remedies for every kind of disease or injury. Companies also promise that the cells will improve appearance or provide a 'rejuvenating' energy boost. The message — that stem-cell therapies need some work, but are an accepted part of medicine — is as clear as it is wrong.

But repeat this mantra enough — as it is repeated endlessly online — and the promises can start to seem real. In some places, they certainly look real. As we reveal on page 149, these 'cures' are offered in real clinics in China, where real nurses and doctors inject people with stem cells in various formulations from various sources — apparently convinced that they are helping patients. It looks and feels routine.

China has tried to crack down on unapproved treatments and it is not the only place where patients can buy these therapies: stem-cell companies also take advantage of gaps in regulation enforcement in the United States (see Nature 483, 13–14; 2012). But in China the problem is more widespread.

Promoters of such unproven and unapproved 'treatments' liken stem-cell therapy to other once-revolutionary therapies, such as organ transplantation. Doctors confess that they can't guarantee that the stem cells will work, but they do guarantee that the procedures are safe. If they weren't, say advocates, we would hear about it. So why not try?

Acceptance is already overtaking clinical evidence, with no systematic follow-up.

This circular logic makes the apparent infiltration of stem-cell technologies into the medical mainstream even more worrisome. The more willing patients and medics are to believe, the less they look for true clinical data, and the less doctors are forced to produce it.

Compare the emergence of stem-cell therapies with the introduction of psychosurgery. Like stem-cell practitioners today, doctors in the 1930s and 1940s felt that the need for lobotomy was urgent enough to bypass the requirement for clinical evidence. Results were reviewed selectively, with pacifying brain damage sometimes taken as a stabilizing 'cure' for schizophrenia or nervous disorders. One promoter even shared the 1949 Nobel Prize in Physiology or Medicine for his part in developing the procedure. There was no long-term follow-up. In the end, doctors mutilated the brains of thousands of patients over the course of decades before critics were able to cast enough doubt on lobotomy to halt its use. The widespread acceptance made it difficult for people to realize that these procedures were actually doing harm: you don't see a problem if you don't bother looking for it.

Of course, there is much legitimate research into stem cells, including many controlled clinical trials. It would be a shame if they were tainted by association with historical failures. However, judging from Nature's investigation in China, acceptance is already overtaking clinical evidence, with no attempt at systematic follow-up of treatments. If stem-cell therapies result in cancer or immunological disease, no one will know.

This does not stop people from outside China flocking to the country to take advantage of the stem-cell therapies offered there and promoted online with glowing endorsements. The clinics are certainly set up to make foreigners feel at home. Set aside from the teeming Chinese hospitals, stem-cell treatment centres have orderly nurse stations, well-lit rooms and good bedside care. What is lacking is controlled clinical trials, reliable data and government approval. If the dedicated medical workers at the clinics don't see the problems, they need to look harder. If they really want to help their patients, they should seek to prove that the treatments work, rather than just assuming that they do.