Editing Radio wave (section)

== Biological and environmental effects ==
{{further|Medical applications of radio frequency}}

Radio waves are ''[[non-ionizing radiation]]'', which means they do not have enough energy to separate [[electron]]s from [[atom]]s or [[molecule]]s, [[ionizing]] them, or break [[chemical bond]]s, causing chemical reactions or [[DNA damage]]. The main effect of absorption of radio waves by materials is to heat them, similarly to the [[infrared]] waves radiated by sources of heat such as a [[space heater]] or wood fire. The oscillating electric field of the wave causes [[polar molecule]]s to vibrate back and forth, increasing the temperature; this is how a [[microwave oven]] cooks food. Radio waves have been applied to the body for 100&nbsp;years in the medical therapy of [[diathermy]] for deep heating of body tissue, to promote increased blood flow and healing. More recently they have been used to create higher temperatures in [[hyperthermia therapy]] and to kill cancer cells.

However, unlike infrared waves, which are mainly absorbed at the surface of objects and cause surface heating, radio waves are able to penetrate the surface and deposit their energy inside materials and biological tissues. The depth to which radio waves penetrate decreases with their frequency, and also depends on the material's [[resistivity]] and [[permittivity]]; it is given by a parameter called the ''[[skin depth]]'' of the material, which is the depth within which 63% of the energy is deposited. For example, the 2.45&nbsp;GHz radio waves (microwaves) in a microwave oven penetrate most foods approximately {{val|2.5|to|3.8|u=cm}}.
[[File:Radio waves hazard symbol.svg|thumb|Radio waves symbol ]]

Looking into a source of radio waves at close range, such as the [[waveguide]] of a working radio transmitter, can cause damage to the lens of the eye by heating. A strong enough beam of radio waves can penetrate the eye and heat the lens enough to cause [[cataract]]s.<ref name="Kitchen-2001">{{cite book |last=Kitchen |first=Ronald |url=https://archive.org/details/rfmicrowaveradia0000kitc |title=RF and Microwave Radiation Safety Handbook |date=2001 |publisher=Newnes |isbn=0750643552 |edition=2nd |pages=[https://archive.org/details/rfmicrowaveradia0000kitc/page/64 64]–65 |url-access=registration}}</ref><ref name="VanderVorst">{{cite book |last1=van&nbsp;der&nbsp;Vorst |first1=André |url=https://books.google.com/books?id=lV3FPLJoyzMC&pg=PA121 |title=RF/Microwave Interaction with Biological Tissues |last2=Rosen |first2=Arye |last3=Kotsuka |first3=Youji |date=2006 |publisher=John Wiley & Sons |isbn=0471752045 |pages=121–122 |access-date=2018-02-14 |archive-url=https://web.archive.org/web/20240922182359/https://books.google.com/books?id=lV3FPLJoyzMC&pg=PA121#v=onepage&q&f=false |archive-date=2024-09-22 |url-status=live}}</ref><ref name="Graf-2001">{{cite book |last1=Graf |first1=Rudolf F. |url=https://books.google.com/books?id=Tc_ACUbCqqQC&pg=PA234 |title=Build Your Own Low-power Transmitters: Projects for the Electronics Experimenter |last2=Sheets |first2=William |date=2001 |publisher=Newnes |isbn=0750672447 |pages=234 |access-date=2018-02-14 |archive-url=https://web.archive.org/web/20240922182241/https://books.google.com/books?id=Tc_ACUbCqqQC&pg=PA234#v=onepage&q&f=false |archive-date=2024-09-22 |url-status=live}}</ref><ref name="Elder-1984">{{cite book |last1=Elder |first1=Joe Allen |title=Biological Effects of Radiofrequency Radiation |last2=Cahill |first2=Daniel F. |date=1984 |publisher=[[US EPA]] |pages=5.116–5.119 |chapter=Biological Effects of RF Radiation |access-date=2019-08-16 |chapter-url=https://books.google.com/books?id=TKIKAQAAMAAJ&pg=SA5-PA116 |archive-url=https://web.archive.org/web/20240922182241/https://books.google.com/books?id=TKIKAQAAMAAJ&pg=SA5-PA116 |archive-date=2024-09-22 |url-status=live}}</ref><ref name="Hitchcock-1995">{{cite book |last1=Hitchcock |first1=R. Timothy |url=https://books.google.com/books?id=lOMWHnZ4h_cC&pg=PA178 |title=Radio-Frequency and ELF Electromagnetic Energies: A handbook for health professionals |last2=Patterson |first2=Robert M. |date=1995 |publisher=John Wiley & Sons |isbn=9780471284543 |series=Industrial Health and Safety Series |pages=177–179 |access-date=2018-02-14 |archive-url=https://web.archive.org/web/20240922182241/https://books.google.com/books?id=lOMWHnZ4h_cC&pg=PA178#v=onepage&q&f=false |archive-date=2024-09-22 |url-status=live}}</ref>

Since the heating effect is in principle no different from other sources of heat, most research into possible health hazards of exposure to radio waves has focused on "nonthermal" effects; whether radio waves have any effect on tissues besides that caused by heating. Radiofrequency electromagnetic fields have been classified by the [[International Agency for Research on Cancer]] (IARC) as having "limited evidence" for its effects on humans and animals.<ref>{{cite press release |title=IARC Classifies Radiofrequency Electromagnetic Fields as Possibly Carcinogenic to Humans |date=31 May 2011 |publisher=[[WHO]] |url=https://www.iarc.fr/wp-content/uploads/2018/07/pr208_E.pdf |access-date=9 Jan 2019 |url-status=live |archive-url=https://web.archive.org/web/20181212062859/https://www.iarc.fr/wp-content/uploads/2018/07/pr208_E.pdf |archive-date=2018-12-12 |website=www.iarc.fr}}</ref><ref>{{cite web |date=9 Nov 2018 |title=Agents Classified by the IARC Monographs |url=https://monographs.iarc.fr/agents-classified-by-the-iarc/ |url-status=live |archive-url=https://web.archive.org/web/20190906143757/https://monographs.iarc.fr/agents-classified-by-the-iarc/ |archive-date=6 September 2019 |access-date=9 Jan 2019 |website=monographs.iarc.fr |series=Volumes&nbsp;1–123 |publisher=[[International Agency for Research on Cancer|IARC]] |language=en-US}}</ref> There is weak mechanistic evidence of cancer risk via personal exposure to RF-EMF from mobile telephones.<ref>{{cite web |last1=Baan |first1=R. |last2=Grosse |first2=Y. |last3=Lauby-Secretan |first3=B. |last4=El Ghissassi |first4=F. |date=2014 |title=Radiofrequency Electromagnetic Fields: Evaluation of cancer hazards |url=https://monographs.iarc.fr/wp-content/uploads/2018/06/REF_Poster2012.pdf |url-status=live |archive-url=https://web.archive.org/web/20181210154717/https://monographs.iarc.fr/wp-content/uploads/2018/06/REF_Poster2012.pdf |archive-date=2018-12-10 |access-date=9 Jan 2019 |website=monographs.iarc.fr |publisher=[[International Agency for Research on Cancer|IARC]] |type=conference poster}}</ref>

Radio waves can be shielded against by a conductive metal sheet or screen, an enclosure of sheet or screen is called a [[Faraday cage]]. A metal screen shields against radio waves as well as a solid sheet as long as the holes in the screen are smaller than about {{frac|1|20}} of [[wavelength]] of the waves.<ref name="Gerke">{{cite book |last1=Kimmel |first1=William D. |url=https://books.google.com/books?id=9PlKDwAAQBAJ&pg=SA6-PA67 |title=Electromagnetic Compatibility in Medical Equipment: A Guide for Designers and Installers |last2=Gerke |first2=Daryl |date=2018 |publisher=Routledge |isbn=9781351453370 |pages=6.67 |access-date=2018-02-15 |archive-url=https://web.archive.org/web/20240922183250/https://books.google.com/books?id=9PlKDwAAQBAJ&pg=SA6-PA67#v=onepage&q&f=false |archive-date=2024-09-22 |url-status=live}}</ref>