Electric and magnetic fields are invisible areas of energy produced wherever electricity exists. An electric field forms around any electrically charged object, even when it’s sitting still. A magnetic field appears when that charge starts moving. Together, they’re often referred to as electromagnetic fields, or EMFs, and they surround everything from the wiring in your walls to the Earth itself.
How Electric Fields Work
An electric field exists around any object that carries a voltage, which is essentially a difference in electrical charge between two points. The higher the voltage, the stronger the field. A key detail: electric fields are present whether or not electricity is actually flowing. The live wire behind your light switch produces an electric field 24 hours a day, even when the switch is off and no current runs through it. In a typical household running on 240 volts (or 120 volts in the US), every energized wire and plugged-in cord generates a low-level electric field in the surrounding space.
Electric fields weaken quickly with distance. Most common building materials, like wood, drywall, and brick, partially block them as well. This means the electric field from wiring inside a wall drops off sharply by the time it reaches the center of a room.
How Magnetic Fields Work
A magnetic field only appears when electric charge is in motion. Inside a wire, that motion is the flow of current. The greater the current, the stronger the magnetic field. This is why a magnetic field around an appliance spikes when it’s switched on and drawing power, unlike an electric field, which is there regardless.
Moving charges don’t just respond to magnetic fields; they create them. When electrons flow through a wire, they generate a magnetic field that circles around the wire. This principle is the foundation of electric motors, transformers, and generators. Unlike electric fields, magnetic fields pass easily through most walls and common materials, making them harder to shield against.
Units and Measurement
Electric field strength is measured in volts per meter (V/m). Magnetic field strength is measured in units called tesla (T). Because everyday magnetic fields are extremely small compared to one full tesla, you’ll usually see them expressed in microtesla (µT), where one microtesla is one millionth of a tesla. An older but still common unit is the gauss (G) or milligauss (mG). The conversion is simple: 1 milligauss equals 0.1 microtesla.
Natural and Everyday Sources
The Earth itself produces a magnetic field that ranges from about 25 to 65 microtesla at the surface, depending on your location. This geomagnetic field is what makes compass needles point north. It’s a static field, meaning it stays essentially constant over time rather than oscillating back and forth.
Inside your home, the picture is different. The electricity running through your walls operates as alternating current (AC), which reverses direction many times per second (60 times per second in the US, 50 in most other countries). This creates time-varying fields that rise and fall in sync with the current. Background magnetic field levels in a typical home sit around 0.1 µT. Near certain appliances, though, instantaneous values can jump to a few hundred microtesla, and electric fields can reach several hundred volts per meter. Hair dryers, vacuum cleaners, electric blankets, and microwave ovens are among the stronger household sources. These fields drop off steeply as you step away from the appliance.
Static Fields vs. Alternating Fields
Static fields stay constant over time. A refrigerator magnet, the Earth’s geomagnetic field, and a battery-powered flashlight (which runs on direct current) all produce static fields. Alternating fields, by contrast, change strength and direction in a repeating cycle. Anything connected to your home’s AC power supply produces alternating fields. The distinction matters because the two types interact with the body differently and are evaluated under separate safety guidelines.
How Fields Weaken With Distance
Both electric and magnetic fields obey the inverse square law, at least in idealized conditions. This means that if you double your distance from a source, the field intensity drops to roughly one quarter of what it was. Triple the distance, and it falls to about one ninth. In practice, the geometry of real-world sources (like a long power line versus a small appliance) changes the math slightly, but the core principle holds: moving even a short distance away from any EMF source makes a large difference in your exposure.
Where EMFs Sit on the Electromagnetic Spectrum
Electric and magnetic fields from power lines and household wiring occupy the extremely low frequency (ELF) end of the electromagnetic spectrum. This is the lowest-energy portion, far below radio waves, microwaves, visible light, and X-rays. The critical dividing line on the spectrum is between non-ionizing and ionizing radiation. Ionizing radiation, which includes X-rays and gamma rays, carries enough energy to knock electrons off atoms and damage DNA directly. Everything below ultraviolet light on the spectrum, including all household and power-line EMFs, is non-ionizing. It does not carry enough energy to break chemical bonds in your body’s cells.
What the Evidence Says About Health
The World Health Organization has reviewed the evidence on long-term exposure to extremely low frequency fields. For electric fields at the levels the general public typically encounters, the WHO concluded there are no substantive health issues. The magnetic field question has gotten more attention because of a statistical association observed in some studies between higher-than-average residential magnetic field exposure and childhood leukemia. After formal risk assessment, however, the WHO determined that this evidence is not strong enough to be considered causal.
For other conditions that have been investigated, including cardiovascular disease and breast cancer, the evidence is even weaker. In some cases, the data actively suggest that ELF fields do not cause these diseases. International bodies that set exposure limits have reviewed the same research and concluded that the evidence does not justify lowering current safety thresholds. The WHO has also noted that, given the weakness of the link between ELF magnetic fields and childhood leukemia, it remains unclear whether reducing exposure would produce any measurable health benefit.
Practical Ways to Reduce Exposure
Because field strength drops so rapidly with distance, the simplest way to lower your exposure is to increase the gap between you and the source. Sitting a foot or two farther from a running appliance can cut the magnetic field you experience by a large factor. Unplugging devices you aren’t using eliminates their magnetic fields entirely (though the electric field from the wall wiring remains). Electric blankets, which sit directly against the body for hours, tend to produce more personal exposure than most other household items simply because of that proximity. Using them to warm the bed and then unplugging before sleep is one common approach.
For most people in a typical home, background EMF levels are far below any threshold that international guidelines flag as concerning. The fields from everyday appliances, wiring, and electronics are a normal part of living with electricity, and they weaken to negligible levels within a short distance from the source.