Electromagnetic fields: sources and health effects
Updated 15 May 2026
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This webpage provides advice on exposure to electric, magnetic and electromagnetic fields typically found in the public environment.
Electromagnetic fields (EMFs) belong to the category of non-ionising radiation (NIR). This is the term given to the part of the electromagnetic spectrum where there’s insufficient quantum energy to cause ionisations in living matter.
EMFs are described as waves, where their amplitude oscillates with time. The number of wave cycles per second is called the frequency and is measured in Hertz (Hz). EMFs discussed in these pages refer to the frequency range from 0 Hz (also known as static fields) to 300 GHz (1 GHz = 1,000,000,000 Hz).
Electric fields are measured in volts per metre (V m-1). Magnetic fields are measured in a unit called tesla. A tesla is a very big unit and the fields usually encountered in the public environment are measured in millionths of a tesla or microtesla (µT).
At low frequencies, including the 50 Hz frequency used for electricity distribution, the electric and magnetic fields components of EMFs are essentially independent from each other and the coupling between electric and magnetic fields is weak. At these frequencies, energy remains in the vicinity of the EMF source.
At high frequencies, including those used for mobile communications, electric and magnetic fields combine and travel outwards from the source. This combination of propagating fields is known as an electromagnetic wave, which transports energy away from the source.
Units of electric and magnetic fields
| Quantity | Unit |
|---|---|
| Electric field strength | volt per metre (V m-1) |
| 1,000 volts per metre = 1 kilovolt per metre (kV m-1) | |
| Magnetic flux density | tesla (T) |
| 1 tesla = 1,000 millitesla (mT) | |
| 1 millitesla = 1,000 microtesla (µT) | |
| 1 microtesla = 1,000 nanotesla (nT) | |
| Frequency | hertz (Hz) |
| 1 kilohertz = 1,000 Hz (kHz) | |
| 1 megahertz = 1,000,000 Hz (MHz) | |
| 1 gigahertz = 1,000,000,000 Hz (GHz) |
Exposure to electromagnetic fields
Central to UKHSA advice is that exposures to electric and magnetic fields should comply with the guidelines published by the International Commission on Non-Ionizing Radiation Protection (ICNIRP).
Public exposure is typically well below the ICNIRP guidelines.
More information about how electromagnetic fields exposure is managed in the UK can be found in Electromagnetic Fields: Policies and regulations.
Further information
Chapter 14 of UKHSA’s Living with radiation document provides background information on electromagnetic fields.
Static fields
Electric fields describe the force exerted on a charge due to the presence of other charges. Thus, electric fields are present wherever there is a charge.
Magnetic fields, on the other hand, describe the interaction between moving charges. As a result, magnetic fields are present wherever there is an electric current.
When the charge distribution or electric current do not vary with time, such as in direct current (DC) electricity distribution, the fields are referred to as static fields.
Sources of static fields
Static electric and magnetic fields include the natural fields that occur in the atmosphere and the man-made fields produced by direct current electricity, including trains and trams, and from magnetic resonance imaging (MRI) scanners.
The Earth’s magnetic field is about 50 µT in the UK. Typical exposures from MRI scanners in hospitals are of the order of up to a few tesla.
Health effects of exposure to static fields
Static electric fields do not penetrate the body, but exposure can result in movement of the hairs on the head and body, which can become annoying above a certain threshold (25 kV m-1). Indirect effects, such as spark discharges (microshocks) may also occur when touching conducting objects exposed to a strong electric field.
Rapid movement in a strong static magnetic field, such as the ones encountered in MRI scanners, can induce electric fields and currents in the body, resulting in transient effects such as vertigo, nausea and a metallic taste in the mouth.
Related documents
Low frequency electric and magnetic fields
Electric fields come from the voltage that is used to make electric current flow in a wire. The voltage is like the water pressure which makes water flow in a plumbing system, and the electric current is like the water flow. Electric fields get bigger as the voltage increases. As the voltage is always present in the mains wiring, the cable to an appliance will always produce an electric field unless the wall switch is off or the appliance is unplugged.
Magnetic fields are produced by electricity flowing as the electric current in a wire. The larger the current, the stronger the magnetic field.
Sources of low frequency electric and magnetic fields
Low frequency electric and magnetic fields come from the generation, distribution and use of electricity. In the UK electricity is generated at a frequency of 50 Hz, or 50 cycles per second, so electric and magnetic fields are also produced at 50 Hz. This is also referred to as power frequency.
The large power lines across the UK operate at 400 or 275 thousand volts (kilovolts or kV). Smaller local lines operate at 132 kV, 66 kV, 33 kV, 11 kV and the domestic supply of 230 V. The electric and magnetic fields in homes mostly come from appliances, house wiring, low-voltage distribution circuits including cables carrying electricity into homes, and substations.
Electric and magnetic fields are also produced by electric transport.
Typical exposure levels to low frequency electric and magnetic fields
The typical background range in UK homes is 1 to 20 V m-1 and this may increase to a few hundred volts per metre very close to domestic appliances and power cables, and up to a few thousand volts per metre, outdoors under large power lines. Most building materials screen out electric fields very effectively and so strong electric fields outside a building do not cause strong fields inside.
The background magnetic field level measured away from appliances usually comes from the local electricity distribution cables which supply the house. The typical background magnetic field level in homes is usually in the range 0.01 to 0.2 µT. The highest magnetic fields in homes usually occur close to electrical appliances and the electrical wiring, even if it is inside the walls. Magnetic fields of up to a few tens of microteslas can occur very close to appliances. In homes within a few tens of metres of large power lines, magnetic field levels are typically a few microteslas but under the largest lines may sometimes reach up to a few tens of microteslas.
Health effects of exposure to electric and magnetic fields
Power frequency electric and magnetic fields can induce electrical currents inside the body. The magnetic fields can cause faint flickering visual sensations (called phosphenes) or even stimulate nerves and muscles, although these effects occur at levels many thousands of times higher than those encountered in buildings.
Electric fields also produce electric charges on the surface of the body. Some people notice the strong electric fields found outdoors beneath large power lines, through hair standing on end. Under some circumstances, people can experience microshocks, like a static shock, coming from contact with objects in strong electric fields. These effects only occur at field levels much higher than those encountered in homes.
Long-term effects of exposure to electric and magnetic fields
A lot of research has been carried out into the possibility that electric or magnetic fields can cause cancer or other serious illnesses.
The results of some studies of human populations have suggested that there may be a two-fold excess in the risk of childhood leukaemia at higher than usual magnetic field exposures in homes (with average values above 0.3 to 0.4 µT), some of which are near to large power lines. It is estimated that around 2 to 5 cases from the total of around 500 cases of childhood leukaemia per year in the UK may be attributable to magnetic fields. This number is based on the assumption that exposure has to be above a certain threshold before there could be a health effect. The overall evidence, however, is not strong enough to draw a firm conclusion that magnetic fields cause childhood leukaemia.
Studies have also looked at whether exposure is linked to the risk of other illnesses such as Alzheimer’s disease. Although there have been some results suggesting a link, the overall balance of evidence is towards no effect and much weaker than that for childhood leukaemia.
The types of studies that investigate these risks face many difficulties, including the possibility of chance, bias and the presence of confounding factors that may confuse the findings. Importantly there is no known mechanism or clear experimental evidence to explain how these effects might happen.
In 2002, the International Agency for Research on Cancer (IARC) classified low frequency electric fields as “not classifiable as to their carcinogenicity in humans” (Group 3), and low frequency magnetic fields as “possibly carcinogenic to humans” (Group 2B).
If you are concerned about your exposure to low frequency electric and magnetic fields, UKHSA has published some guidance on steps you can take to minimise your exposure.
Radio waves
Radio frequency electromagnetic fields are often termed radiofrequency (RF) fields or simply radio waves. Radio wave frequencies range from 100 kHz up to 300 GHz.
As frequency increases the electric and magnetic fields from a source become more coupled together and dependent on each other. This means it is not necessary to measure both fields, as a measurement of only one component is enough to calculate the other.
Sources
Sources of radio waves are used in broadcasting and telecommunications, including TV and radio, radar and satellite communications, mobile and cordless phones, Wi-Fi devices, and microwave ovens.
They are also used in industrial applications to heat, weld and cure objects and materials. There can be a low level of exposure to radio waves everywhere that radio, television, or mobile phone signals are received. Higher exposures can occur when in immediate proximity to transmitting sources, such as when mobile phones are used to make voice calls and held close to the head.
More information on commonly found radio wave sources is available on the following links:
Health effects of exposure to radio waves
The main biological effect of exposure to radio waves is heating. This results primarily from the alignment and relaxation of electrically polarised molecules, mostly water, in the body. Such heating is not uniform, as living tissues with a high-water content, such as muscle, absorb power more than tissues with a low water content such as fat. Local blood flow through the tissues will also influence the temperature rise.
At frequencies from about 100 kHz to 10 MHz, exposure can also induce currents within the body which result in induction heating. Under these conditions, any increases in temperature are much more likely to occur in narrow parts of the body such as the ankles or wrists.
At frequencies above 10 GHz, heating is largely confined to the surface of the body. This is because as frequency increases, the fields’ penetration into the body decreases. In addition, pulsed fields of sufficient intensity between 200 MHz and 6 GHz can be sensed as a buzzing or clicking noise. This is thought to be caused by a small but rapid increase in temperature in the tissues in the head when the energy is absorbed. This generates a sound wave that stimulates the cochlea and may be annoying if prolonged, although there is no evidence that this effect is harmful.
Finally, touching conducting objects in fields below 300 MHz can give rise to burns. These are caused by the flow of current to the body through a small area of contact, such as a fingertip. Usually, members of the public are not exposed to fields with such strength that they experience these effects.
Long-term effects of exposure to radio waves
The International Agency for Research on Cancer (IARC) reviewed the health effects of exposure to radio waves in May 2011 and concluded that such exposures are “possibly carcinogenic” to humans (Group 2B), based on IARC’s classification scheme. The IARC classification for radio waves was largely based on personal exposures associated with mobile phone use and the evidence was evaluated as being limited among users of wireless telephones for glioma and acoustic neuroma (cancers of brain or nerve tissues in the head), and inadequate to draw conclusions for other types of cancers. The evidence from environmental radiofrequency exposures, which include wireless telecommunications, was considered inadequate to draw conclusions.
The World Health Organization (WHO) states that, to date, and after much research has been carried out, no adverse health effect has been causally linked with exposure to wireless technologies.
The European Commission has scientific expert committees to provide it with advice on aspects of public health. The Scientific Committee on Health, Environmental and Emerging Risks (SCHEER) has produced several reports, known as ‘opinions’, in which it expressed views broadly in line with those of UKHSA, ICNIRP and WHO. The most recent SCHEER opinion was published in April 2023 and contains detailed conclusions on different aspects of the scientific evidence.
If you are concerned about your exposure to radio waves, UKHSA has published some guidance on steps you can take to minimise your exposure.