Abstract
In a comment to our publication Mobile phone headache: A double-blind, sham-controlled provocation study (1), Chu (2) discusses the provocation procedure. It is suggested that provocations with radio frequency (RF) electromagnetic fields to explore possible effects on ‘mobile phone headache’ should be done in combination with background noise and heating of the area around the ear. In our study, individuals usually experiencing mobile phone headache were exposed to RF fields alone.
In addition to the nocebo effect, a range of other potential reasons for experienced mobile phone headache can be of interest. Skin heating and background noise were mentioned by Chu (2), but also others can be added like stress in connection with the phone call and muscle strain by holding the phone. Such factors may or may not be present, and they will also have different characteristics when present. The background noise level can, for example, vary from a very high to a very low level. Furthermore, the noise could be from road traffic, music or other sources with quite different spectral content. It would be a challenge to select the most relevant characteristics of the co-factors or to test multiple factor combinations. A high number of tests would probably be required.
However, in some studies, possible synergy effects have been taken into account. Hillert et al. (3) added heat to RF fields generated by a mobile phone. Headache was more commonly reported after RF exposure than after sham, due to an increase in the non-symptomatic control group, i.e. no effect was found for those who regarded themselves to be hypersensitive to the electromagnetic fields from mobile phones. The effect on the non-symptomatic group has to be confirmed by other studies. Eltiti et al. (4) and Wallace et al. (5) used RF fields from mobile phone base station antennae in combination with mental load to provoke stress. They found no effect on well-being or symptoms.
Another relevant co-factor to include is the low frequency (LF) electromagnetic fields generated by the current pulses from GSM phones (as was used in our study as well as in most published similar ones). However, there are indications that some individuals experience complaints in connection with mobile phone calls but not when being near or using sources emitting only LF fields (e.g. Oftedal et al. (6)), i.e. indicating a role of the RF fields. Reports about various symptoms including headache in connection with RF fields from mobile phone base station antennae (e.g. Hutter et al. (7)) suggest that potential co-factors like skin heating and background noise are not required for the experience of headaches and other symptoms associated with electromagnetic fields. Therefore, we found it highly relevant to explore the effect of the RF electromagnetic fields from mobile phones alone, without adding other factors that potentially would influence the result.
Summarizing, we found no indication of an effect on headache from the RF fields used in the GSM mobile phones. This is in line with the results of earlier and later similar studies (8), among which most included both LF and RF fields. However, as also recognised by Chu (2), we (1,9) as well as others (8,10) have found indications that the nocebo effect probably is one of the factors responsible for mobile phone attributed headache.