The growing market for brain screening tests, which people can buy as part of a general health MOT, has raised doubts about the need for brain scans.
Researchers warn that paid-for brain scans - increasingly popular with healthy people who want to allay fears about undiagnosed brain cancer and stroke - may do more harm than good.
They reach their conclusion having analysed the results of almost 20,000 brain scans from people who undertook the tests for a variety of reasons, such as general health MOTs or volunteering for medical research. None of them had any symptoms suggesting that they had an underlying brain condition.
The researchers found that almost three per cent of healthy people had an abnormality on a brain MRI scan and warn that even when an incidental abnormality - such as a weakened blood vessel in the brain or a benign tumour - is discovered, there is no clear medical evidence that treatment would do more good than harm.
The experts say this lack of evidence can create anxiety, with many patients feeling that a tough choice has to be made between risky, potentially unnecessary surgery or leaving their condition untreated.
Dr Rustam Al-Shahi Salman, an MRC clinician scientist at the University of Edinburgh, said: "The difficulty with these health check-ups is that in the small number of people who do harbour some undiagnosed brain condition, there is not a clear next step.
"We do not have enough medical evidence to know whether we should treat the abnormalities or just leave them be. Until we have that knowledge, we cannot be sure that commercial screening benefits people with incidental findings on their brain scan. Furthermore, there is little evidence that "peace of mind" lasts for the people with normal brain scans."
The results of the study have been published in the British Medical Journal
and represent the largest review of brain scanning results ever to be conducted.