Mobile telephone effect. Artwork showing the microwave exposure levels in a person's head and hand whilst they are using a mobile telephone (blue). This exposure may cause cancer and changes in hormone levels. The exposure levels, measured in watts per kilogramme (W/kg), are colour-coded: 1 W/kg (yellow); 0.06 W/kg (light orange); 0.004 W/kg (dark orange); 2 millionths of a W/kg (red); unexposed areas (brown). The exposure levels fall exponentially with increasing distance, but some microwaves pass through the skull & muscle to pen- etrate into the brain. A typical mobile telephone emits about 200 milliwatts of microwaves, about half of which are absorbed in the user's head.