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Electromagnetic fields and public health.
Base stations and wireless technologies
WHO Fact sheet N°304 May 2006
Mobile telephony is now commonplace around the world. This wireless technology
relies upon an extensive network of fixed antennas, or base stations, relaying
information with radiofrequency (RF) signals. Over 1.4 million base stations
exist worldwide and the number is increasing significantly with the introduction
of third generation technology.
Other wireless networks that allow high-speed internet access and services, such
as wireless local area networks (WLANs), are also increasingly common in homes,
offices, and many public areas (airports, schools, residential and urban areas).
As the number of base stations and local wireless networks increases, so does
the RF exposure of the population. Recent surveys have shown that the RF
exposures from base stations range from 0.002% to 2% of the levels of
international exposure guidelines, depending on a variety of factors such as the
proximity to the antenna and the surrounding environment. This is lower or
comparable to RF exposures from radio or television broadcast transmitters. |
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Some Interesting Cell Phone Facts
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There has been concern about
possible health consequences from exposure to the RF fields produced by wireless
technologies. This fact sheet reviews the scientific evidence on the health
effects from continuous low-level human exposure to base stations and other
local wireless networks.
Health concerns
A common concern about base station and local wireless network antennas
relates to the possible long-term health effects that whole-body exposure to the
RF signals may have. To date, the only health effect from RF fields identified
in scientific reviews has been related to an increase in body temperature (> 1
°C) from exposure at very high field intensity found only in certain industrial
facilities, such as RF heaters. The levels of RF exposure from base stations and
wireless networks are so low that the temperature increases are insignificant
and do not affect human health.
The strength of RF fields is greatest at its source, and diminishes quickly with
distance. Access near base station antennas is restricted where RF signals may
exceed international exposure limits. Recent surveys have indicated that RF
exposures from base stations and wireless technologies in publicly accessible
areas (including schools and hospitals) are normally thousands of times below
international standards.
In fact, due to their lower frequency, at similar RF exposure levels, the body
absorbs up to five times more of the signal from FM radio and television than
from base stations. This is because the frequencies used in FM radio (around 100
MHz) and in TV broadcasting (around 300 to 400 MHz) are lower than those
employed in mobile telephony (900 MHz and 1800 MHz) and because a person's
height makes the body an efficient receiving antenna. Further, radio and
television broadcast stations have been in operation for the past 50 or more
years without any adverse health consequence being established.
While most radio technologies have used analog signals, modern wireless
telecommunications are using digital transmissions. Detailed reviews conducted
so far have not revealed any hazard specific to different RF modulations.
Cancer: Media or anecdotal reports of cancer clusters around mobile phone base
stations have heightened public concern. It should be noted that geographically,
cancers are unevenly distributed among any population. Given the widespread
presence of base stations in the environment, it is expected that possible
cancer clusters will occur near base stations merely by chance. Moreover, the
reported cancers in these clusters are often a collection of different types of
cancer with no common characteristics and hence unlikely to have a common cause.
Scientific evidence on the distribution of cancer in the population can be
obtained through carefully planned and executed epidemiological studies. Over
the past 15 years, studies examining a potential relationship between RF
transmitters and cancer have been published. These studies have not provided
evidence that RF exposure from the transmitters increases the risk of cancer.
Likewise, long-term animal studies have not established an increased risk of
cancer from exposure to RF fields, even at levels that are much higher than
produced by base stations and wireless networks.
Other effects: Few studies have investigated general health effects in
individuals exposed to RF fields from base stations. This is because of the
difficulty in distinguishing possible health effects from the very low signals
emitted by base stations from other higher strength RF signals in the
environment. Most studies have focused on the RF exposures of mobile phone
users. Human and animal studies examining brain wave patterns, cognition and
behaviour after exposure to RF fields, such as those generated by mobile phones,
have not identified adverse effects. RF exposures used in these studies were
about 1000 times higher than those associated with general public exposure from
base stations or wireless networks. No consistent evidence of altered sleep or
cardiovascular function has been reported.
Some individuals have reported that they experience non-specific symptoms upon
exposure to RF fields emitted from base stations and other EMF devices. As
recognized in a recent WHO fact sheet "Electromagnetic Hypersensitivity", EMF
has not been shown to cause such symptoms. Nonetheless, it is important to
recognize the plight of people suffering from these symptoms.
From all evidence accumulated so far, no adverse short- or long-term health
effects have been shown to occur from the RF signals produced by base stations.
Since wireless networks produce generally lower RF signals than base stations,
no adverse health effects are expected from exposure to them.
Protection standards
International exposure guidelines have been developed to provide
protection against established effects from RF fields by the International
Commission on Non-Ionizing Radiation Protection (ICNIRP, 1998) and the Institute
of Electrical and Electronic Engineers (IEEE, 2005).
National authorities should adopt international standards to protect their
citizens against adverse levels of RF fields. They should restrict access to
areas where exposure limits may be exceeded.
Public perception of risk
Some people perceive risks from RF exposure as likely and even possibly severe.
Several reasons for public fear include media announcements of new and
unconfirmed scientific studies, leading to a feeling of uncertainty and a
perception that there may be unknown or undiscovered hazards. Other factors are
aesthetic concerns and a feeling of a lack of control or input to the process of
determining the location of new base stations. Experience shows that education
programmes as well as effective communications and involvement of the public and
other stakeholders at appropriate stages of the decision process before
installing RF sources can enhance public confidence and acceptability.
Conclusions
Considering the very low exposure levels and research results collected
to date, there is no convincing scientific evidence that the weak RF signals
from base stations and wireless networks cause adverse health effects.
WHO Initiatives
WHO, through the International EMF Project, has established a programme
to monitor the EMF scientific literature, to evaluate the health effects from
exposure to EMF in the range from 0 to 300 GHz, to provide advice about possible
EMF hazards and to identify suitable mitigation measures. Following extensive
international reviews, the International EMF Project has promoted research to
fill gaps in knowledge. In response national governments and research institutes
have funded over $250 million on EMF research over the past 10 years.
While no health effects are expected from exposure to RF fields from base
stations and wireless networks, research is still being promoted by WHO to
determine whether there are any health consequences from the higher RF exposures
from mobile phones.
The International Agency for Research on Cancer (IARC), a WHO specialized
agency, is expected to conduct a review of cancer risk from RF fields in
2006-2007 and the International EMF Project will then undertake an overall
health risk assessment for RF fields in 2007-2008. |
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