This involves patients travelling to other countries, where medical regulations are less strict, for treatment with unproven and potentially unsafe therapies.
Countries should unite to tackle unscrupulous advertising of unproven stem cell therapies, the experts say.
Hundreds of medical centres world-wide offer therapies involving transplantation of so-called stem cells – claiming they can repair damaged tissues.
Clinics are marketing the treatment for a range of conditions, including multiple sclerosis and Parkinson’s disease.
Often therapies are advertised directly to patients promising a cure. But experts say there is often no evidence to show treatments will help anyone, or will not cause harm.
Researchers say the practice risks undermining the development of rigorously tested, validated therapies, putting lives at risk.
Writing in the journal Science Translational Medicine, the group calls for co-ordinated global action to tackle the problem.
They are also want the World Health Organisation to help guide responsible clinical use of cells and tissues, as it does for medicines and medicinal devices.
Their appeal follows the deaths of two children at a clinic in Germany in 2010, which exploited a legal loophole to offer untested treatments. The clinic has since been closed.
Dr Sarah Chan, a Chancellor’s Fellow at the university, said delays in approving treatments were to protect patients.
“Many patients feel potential cures are held back by red tape and lengthy approval processes.
“Although this can be frustrating, these procedures are there to protect patients from undergoing needless treatments that could put their lives at risk.
“Stem cell therapies hold a lot of promise but we need rigorous clinical trials and regulatory processes to determine whether a proposed treatment is safe, effective and better than existing treatments.”
Some rigorously tested types of stem cell transplantation – mainly blood and skin stem cells – have been approved to treat certain types of cancer and to grow skin grafts for patients with severe burns.