Radio waves play a role in almost everything we do when we are connected. Phone calls, GPS navigation, video streaming, all of it depends on electromagnetic signals. These technologies make life easier, but they also raise good questions about their impact. Between official recommendations and scientific studies, it is not always easy to know what to think. So how do radio waves actually work, and what does the science say about safe use?
A wave is simply energy moving from one point to another without carrying matter along with it. Toss a stone into a lake and you will see ripples spreading out. The water itself does not travel, but the energy does. Electromagnetic waves work in the same way with one important difference. They can move through empty space. That is why satellites can send data to Earth and why phones can pick up a signal. The French National Frequency Agency (ANFR) classifies waves by frequency, which determines their energy and behavior. On the spectrum you will find radio waves at the low end, visible light in the middle, and X-rays and gamma rays at the high end.
Although they all follow the principle of "all waves transfer energy, but they do not transfer matter", they are part of a vast family within which categories with various physical properties can be distinguished:
- Mechanical waves: these require a material support (solid, liquid, or gas), like a stretched elastic band that oscillates or vibrates to generate mechanical waves that pass through the rubber.
- Electromagnetic waves (OEM): these can move without a material support. The electromagnetic spectrum extends from the lowest frequencies (those of power lines, for example) to the highest (UV, X-rays, gamma rays). In between are radio waves (or radio frequencies), which are naturally present and used in communications and, of course, by light: everything our eye sees is transmitted by OEMs whose frequency corresponds to the "visible" band of the spectrum.
Scientists use the Specific Absorption Rate (SAR) to measure how much the body absorbs from radio waves. ANFR expresses SAR in watts per kilogram (W/kg).
In Europe, the limits are:
- Head and torso: maximum 2 W/kg
- Limbs: maximum 4 W/kg
These limits include wide safety margins. For comparison, the human body naturally produces about 100 watts of heat at rest, far more than the energy absorbed from radio waves. Each year, the ANFR tests more than 100 types of smartphone sold in France to ensure the limits are respected. In 2022, out of 102 phones tested, the median head-SAR was 0.44 W/kg, five times lower than the limit. The International Agency for Research on Cancer (IARC) has placed radio frequencies in Group 2B, meaning possibly carcinogenic. That reflects limited evidence without proof of a direct link. Coffee and pickled vegetables are in the same category.
Modern devices are designed to keep emissions as low as possible. Smartphones constantly adjust their power depending on how close they are to the nearest cell tower. A stronger signal means less power needed. This is why more antennas can actually reduce overall exposure. Regarding 5G, ANFR testing shows no meaningful increase in SAR. On average, 5G frequencies are only used about 20 percent of the time, and the technology itself is more energy efficient. 5G also uses directional beams that send the signal directly to the user instead of broadcasting everywhere, which improves performance and reduces unnecessary exposure. Being near a cell tower usually means much lower exposure, often 100 to 1000 times less, than holding a phone to your ear. Towers spread signals over a wide area, while phones transmit close to the body.
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