There is growing concern, especially in Europe, about the potential for harm arising out of the effects of the absorbtion of mobile phone microwave radiation in the brain of the user. In particular, both the use of unidirectional aerials and their very close proximity with the cranium have been identified as special risks. It is suggested that a significant proportion (perhaps 40%) of the output of unidirectional aerials is absorbed by the head of the user; and that energy is concentrated around the aerial, which tends to be bare millimeters from the brain.

Mobile phones have been linked with a number of phenomena including short-term and long-term memory loss, increased blood pressure, and brain tumors.

Radiation shields, designed to clip around the body and aerial of mobile phones, absorb and/or reflect microwave energy.