Mobile phone masts are not responsible for the symptoms of ill health some blame them for, a major UK study says.
Dozens of people who believed the masts trigger symptoms such as anxiety, nausea and tiredness could not detect if signals were on or off in trials.
But when they believed the signal was on they reported more distress - indicating a psychological problem.
However, the Environmental Health Perspectives study stressed people were nonetheless suffering "real symptoms".
"Belief is a very powerful thing," said Professor Elaine Fox, of the University of Essex, who led the three year study.
"If you really believe something is going to do you some harm, it will."
The study was funded by the Mobile Telecommunications and Health Research programme,
It is unclear how many people in the UK suffer from "electro-sensitivity", an allergy they believe can be triggered by a range of modern day appliances from hair driers to mobile phone masts. In 2005 the Health Protection Agency (HPA) said there was no scientific evidence to link their ill health with electrical equipment, while acknowledging sufferers could have real and unpleasant symptoms.
But the HPA research did not consider the effects of waves from phone masts, as most of the studies looking at electrical sensitivity were carried out before they were widely introduced.
A number of studies subsequently have looked at the mobile effect, but the Essex experiments are some of the largest and most detailed to date.
After 12 of the sufferers dropped out of the trial researchers tested a total of 44 people with a history of symptoms against a control group of 114 people who had never reported ill effects from masts.
When the signal was being emitted, and they were told of this, sensitive individuals reported lower levels of well-being.
This was true for exposure to both forms of mobile systems - GSM and UMTS (3G).
However, when tests were carried out in which neither the experimenter or participant knew if the mast was on or off the number of symptoms reported was not related to whether a signal was being emitted or not.
Source - BBC