Exposure to the radiofrequency fields generated by mobile phones does not cause head pain or increase blood pressure, according to a Norwegian study.

Instead, people who experience such symptoms do so because they expect that they will occur, the findings suggest.

Dr Gunnhild Oftedal and associates at the Norway University of Science and Technology in Trondheim recruited 17 subjects who "regularly experienced pain or discomfort¹ in the head during or shortly after mobile phone calls lasting² between 15 and 30 minutes."

The participants were tested during mobile phone radiofrequency exposure and sham³ exposure, without knowing which session was which. Each session lasted 30 minutes, and 65 pairs of trials were conducted.

As reported in the medical journal Cephalalgia, the subjects said they felt an increase in pain or discomfort during 68 per cent of all trials. The degree of symptoms was not associated with the order of trials.

The researchers observed no statistically⁴ significant correlations⁵ between actual exposures and the subjects' reports of symptom severity, and no effects of exposure on changes in heart rate or blood pressure.

Oftedal's team concludes that the most likely explanation for the headaches and discomfort reported by the subjects "is that the symptoms are due to negative expectations."