ELECTROMAGNETIC FIELDS AND PUBLIC HEALTH: Physical Properties and Effects on Biological Systems

Fact Sheet N182
Reviewed May 1998

ELECTROMAGNETIC FIELDS AND PUBLIC HEALTH
Physical Properties and Effects on Biological Systems
Natural and many human-made sources generate electromagnetic energy in the form ofelectromagnetic waves. These waves consist of oscillating electric and magnetic fields
which interact differently with biological systems such as cells, plants, animals, orhuman beings. In order to better understand these interactions, it is essential to be familiar
with the physical properties of the waves which make up the electromagnetic spectrum.
Electromagnetic waves can be characterized by their wavelength, frequency, or energy.
The three parameters are interrelated. Each influences the effect the field may have on abiological system.
The frequency of an electromagnetic wave is simply the number of oscillations
which passes a fixed point per unit of time. It is measured in cycles per second, orhertz. One cycle per second equals one hertz (Hz). Large divisions commonly used
to describe radio frequency (RF) fields include the kilohertz (kHz), or one
thousand cycles per second; the megahertz (MHz), one million cycles per second;
and the gigahertz (GHz), one billion cycles per second.
The shorter the wavelength, the higher the frequency. The middle of the AM
broadcast band, for example, has a frequency of one million hertz (1 MHz) and awavelength of about 300 metres. Microwave ovens use a frequency of 2.45 billion
hertz (2.45 GHz) and a wavelength of 12 centimetres.
An electromagnetic wave consists of very small packets of energy called photons.
The energy in each packet or photon is directly proportional to the frequency of thewave: The higher the frequency, the larger the amount of energy in eachphoton.
How electromagnetic waves affect biological systems is determined partly by theintensity of the field and partly by the amount of energy in each photon.
Electromagnetic waves at low frequencies are referred to as "electromagnetic fields"
and those at very high frequencies are called "electromagnetic radiations". According
to their frequency and energy, electromagnetic waves can be classified as either "ionizing
radiations" or "non-ionizing radiations" (NIR).
Ionizing radiations are extremely high frequency electromagnetic waves (X-rays
and gamma rays), which have enough photon energy to produce ionization (create
positive and negative electrically charged atoms or parts of molecules) by breaking
the atomic bonds that hold molecules in cells together.
Non-ionizing radiations (NIR) is a general term for that part of theelectromagnetic spectrum which has photon energies too weak to break atomic
bonds. They include ultraviolet (UV) radiation, visible light, infrared radiation,radiofrequency and microwave fields, extremely low frequency (ELF) fields, aswell as static electric and magnetic fields.
Even high intensity NIR cannot cause ionization in a biological system. NIR,
however, have been shown to produce other biological effects, for instance, by

ELECTROMAGNETIC FIELDS AND PUBLIC HEALTH: Physical Properties and Effects on Biological Systems

heating, altering chemical reactions or inducing electrical currents in tissues andcells.
Electromagnetic waves may produce biological effects which may sometimes, but notalways, lead to adverse health effects. It is important to understand the difference
between the two:
A biological effect occurs when exposure to electromagnetic waves causes somenoticeable or detectable physiological change in a biological system.
An adverse health effect occurs when the biological effect is outside the normal
range for the body to compensate, and thus leads to some detrimental healthcondition.
Some biological effects can be innocuous, such as the body's reaction of increasing bloodflow in the skin in response to slightly greater heating from the sun. Some effects can beadvantageous, such as the feeling of warmth of direct sunshine on a cool day, or can evenlead to positive health effects, such as the sun's role in helping the body produce vitamin
D. However, some biological effects lead to adverse health effects, such as the pain of
sunburn or skin cancer.
The International EMF Project of the World Health Organization is addressing thehealth concerns raised about exposure to radiofrequency (RF) and microwave fields,intermediate frequencies (IF), extremely low frequency (ELF) fields, and static
electric and magnetic fields. These electromagnetic fields can produce different
biological effects that may lead to health consequences.
Intermediate frequency (IF) and Radiofrequency (RF) fields are known to produce
heating and the induction of electrical currents. Other less established biologicaleffects have also been reported.
Fields at frequencies above about 1 MHz primarily cause heating by moving ionsand water molecules through the medium in which they exist. Even very low levelsof energy produce a small amount of heat, but this heat is carried away by thebody's normal thermoregulatory processes without the person noticing it.
A number of studies at these frequencies suggest that exposure to fields too weakto cause heating may have adverse health consequences, including cancer andmemory loss. Identifying and encouraging coordinated research into these open
questions is one of the major objectives of the International EMF Project.
Fields at frequencies below about 1 MHz primarily induce electrical charges andcurrents which can stimulate cells in tissues such as nerves and muscles. Electricalcurrents already exist in the body as a normal part of the chemical reactions
involved in living. If fields induce currents significantly exceeding this backgroundlevel in the body, there is a possibility of adverse health consequences.
Extremely Low Frequency (ELF) electric and magnetic fields. The primary action in
biological systems by these fields is the induction of electrical charges and currents.
This mechanism of action is unlikely to explain the health effects, such as cancer inchildren, reported to occur from exposure to "environmental" levels of ELF fields.
ELF electric fields exist whenever a charge (voltage) is present, regardless ofwhether any current is flowing. Almost none of the electric field penetrates into thehuman body. At very high field strengths they can be perceived by hair movementon the skin. However, some studies suggest that exposure to low levels of thesefields is associated with an increased incidence of childhood cancer or other healthconsequences. Other studies do not. The International EMF Project isrecommending that more focused research be conducted to improve health risk
assessments.
ELF magnetic fields exist whenever an electric current is flowing. They easily

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ELECTROMAGNETIC FIELDS AND PUBLIC HEALTH: Physical Properties and Effects on Biological Systems

penetrate the human body without any significant attenuation. Someepidemiological studies have reported associations between ELF fields and cancer,
especially in children, but others have not. Research on effects of low-level(environmental) ELF fields is currently underway, including that monitored andencouraged by the International EMF Project.
Static electric and magnetic fields. While the primary action in biological systems bythese fields is the induction of electrical charges and currents, other effects have been
established to occur that could potentially lead to adverse health consequences, but onlyat very high field strengths.
Static electric fields do not penetrate into the body, but can be perceived by skinhair movement. Except for electrical discharges from strong static electric fields,
they do not seem to have significant health effects.
Static magnetic fields have virtually the same strength inside the body as outside.
Very intense static magnetic fields can alter blood flow or change normal nerve
impulses. But such high field strengths are not found in everyday life. However,there is insufficient information about the effects of long-term exposure to static
magnetic fields at levels found in the working environment.
Safety Standards: In order to ensure that human exposure to EMF should not haveadverse health effects, that man-made EMF generating devices are safe and their use does
not electrically interfere with other devices, various international guidelines and standards
are adopted. Such standards are developed following reviews of all the scientific literatureby groups of scientists who look for evidence of consistently reproduced effects withadverse health consequences. These groups then recommend guidelines for standards foraction by the appropriate national and international bodies. A non-governmentalorganization, formally recognised by WHO in the field of NIR protection, is theInternational Commission on Non-Ionizing Radiation Protection (ICNIRP). ICNIRP
has established international guidelines on human exposure limits for all electromagnetic
fields, including ultraviolet (UV) radiation, visible light and infrared radiation, as well as
RF fields and microwaves.
Electromagnetic waves are generated by natural, but mostly by human-made sources.
Their spectrum includes both ionizing and non-ionizing radiations (NIR).
Ionizing radiations (X-rays and gamma rays) have enough energy to create positive
and negative electrically charged atoms or parts of molecules by breaking the atomic
bonds that hold molecules in cells together. This effect is called ionization.
Even high intensity NIR cannot cause ionization in the biological system. NIR,
however, have been shown to produce other biological effects, for instance, by heating,altering normal chemical reactions or inducing electrical currents in tissues.
The International EMF Project of the World Health Organization deals with thehealth effects of static, extremely low frequency (ELF), intermediate frequencies(IF) and radiofrequency (RF) electromagnetic fields (0-300 GHz).
Electromagnetic waves of different frequencies interact differently with biologicalsystems, such as cells, plants, animals, or human beings. The extent they affectbiological systems depends partly on their intensity and partly on the amount ofenergy in photons.
Biological effects produced by electromagnetic waves may sometimes, but not always,
lead to adverse health effects.
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For further information, please contact the Office of Press and Public Relations, WHO,Geneva. Telephone (41 22) 791 2599. Fax (41 22) 791 4858. Email: info@who.int
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this subject can be obtained on Internet on the WHO home page http://www.who.int© WHO/OMS, 1998 |Concept

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