Hearing mechanisms:
The auditory system is divided into 3 parts. The outer ear consists of the external ear (the pinna) and the ear canal. The middle ear is a cavity between the eardrum and the inner ear. It is air-filled and is connected to the back of the throat by the eustachian tube, which opens during swallowing and yawning and allows air to enter the middle ear, thus enabling the pressure in the middle ear to be maintained. The inner ear consists of the cochlea and the vestibular labyrinth. The latter is part of the systems controlling the balance mechanisms of the body.

Sound waves are transmitted by the eardrum through the middle ear as vibrations, which in turn are amplified by a series of small bones, attached to the eardrum at one end and to the oval window of the inner ear at the other. The sound waves are converted to electrical impulses by specialized cells in the cochlea, the outer hair cell (OHC). Pure tone audiometry is used to assess hearing threshold level (HTL), and is sensitive to small changes in outer and inner hair cell function. The impulses are then transmitted to the auditory cortex of the brain in the temporal lobe by the auditory nerve (cranial nerve 8). Auditory brain stem response (ABR) is used to assess this stage in the hearing process.

The OHC generates sounds (otoacoustic emissions, or OAE) because the cells have spontaneous motility, that causes backward energy propagation from the cochlea to the middle ear, and then to the ear canal, where they can be recorded using a special microphone. Cochlear function can be evaluated by using low-intensity stimuli, and the frequency of change in OAE reflects the frequency location of damage to the cochlea. Two commonly measured types of otoacoustic emissions are distortion product emissions (DPOAE), which are evoked by stimulation with two pure tones of different frequencies, and transient emissions (TEOAE), in which the stimulus is an acoustic click of brief duration (Parazzini 2007).

Microwave hearing:
The phenomenon of a microwave-induced auditory sensation in humans and animals is a well-established effect (Lin, 2002). It is thought to be due to the microwave pulse causing a thermoelastic wave of pressure that travels by bone conduction to the inner ear. A single microwave pulse can be perceived as an acoustic click or knocking sound, and a train of microwave pulses to the head can be sensed as an audible tune (Lin, 2002). Elder and Chou (2003) published a detailed review of this subject.

Experiments with exposure to microwaves:
One paper reported no effect on hearing after a 10-minute exposure to EMF from a GSM cell phone (Ozturan, 2002). Uloziene (2005) reported no effect on hearing from a 10-minute exposure to either 900 or 1800 MHz. Janssen (2005) and Parazzini (2005) found no significant change in distortion product otoacoustic emissions levels in response to EMFs at 900 MHz. Parazzini et al. (2007), in a European Commission "Guard" project, found no effects on the auditory system of exposure to GSM phone signals at 900 or 1800 MHz.

Kellenyi, (1999) found changes in the auditory brainstem response after a 15 minute exposure, but no details are given of the SAR in the experiment. Arai (2003), Oysu (2005), Sievert (2005) and Mora (2006), however, found no changes in auditory brainstem responses after exposure to mobile phone signals at 800-900 MHz.

Pau (2005) found no effect on the vestibular function of the ear from exposure to an 889.6 MHz field.

Oktay (2006) tested volunteers who had used their cell phone frequently for 4 years, and compared them with moderate- and non-users. Pure tone audiometry revealed lowering of detection thresholds in some frequencies in the frequent users. However, no allowance was made for other factors that could have influenced the outcome, and the study was not blinded.

References:


Authors
Arai N, Enomoto H, Okabe S, Yuasa K.
Title
Thirty minutes mobile phone use has no short-term adverse effects on central auditory pathways.
Journal
Clin Neurophysiol 2003;114:1390-1394.
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Authors
Balbani APS, Montovani JC.
Title
Mobile phones: influence on auditory and vestibular systems.
Journal
Rev. Bras. Otorrinolaringol 2008;74(1):125-131.


Authors
Janssen T, Boege P, von Mikusch-Buchberg J, Raczek J.
Title
Investigation of potential effects of cellular phones on human auditory function by means of distortion product otoacoustic emissions.
Journal
J Acoust Soc Am 2005;117:1241-7.
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Authors
Kaprana AE, Karatzanis AD, Prokopakis EP, Panagiotaki IE, Vardiambasis IO, Adamidis G, Christodoulou P, Velegrakis GA.
Title
Studying the effects of mobile phone use on the auditory system and the central nervous system: a review of the literature and future directions.
Journal
Eur Arch Otorhinolaryngol. Ahead of print 27 May 2008.


Author
Kellenyi L, Thuroczy GY, Faludy B, Lenard L
Title
Effects of mobile GSM radiotelephone exposure on the auditory brainstem response.
Journal
Neurobiology 1999;7:79-81
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Authors
Kwon MS, Jääskeläinen SK, Toivo T, Hämäläinen H.
Title
No effects of mobile phone electromagnetic field on auditory brainstem response.
Journal
Bioelectromagnetics. Jul 16, 2009 Ahead of print.

Authors
Mora R, Crippa B, Mora F, Dellepiane M.
Title
A study of the effects of cellular telephone microwave radiation on the auditory system in healthy men.
Journal
Ear Nose Throat J 2006;85:162-3.
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Authors
Moulin AM, Parazzini M, Lutman ME, Thuroczy G, Sliwinska-Kowalska M, Tavarkiladze G, Uloziene I, Uloza V, Mishra S, Collet L, Ravazzani P.
Title
Potential adverse effects of UMTS electromagnetic fields generated by mobile phones on the human inner ear: A European project (EMFNEAR).
Journal
J Acoust Soc Am. 2008;123(5):3856.


Authors
Oktay MF, Dasdag S.
Title
Effects of intensive and moderate cellular telephone use on hearing function.
Journal
Electromagnetic Biology and Medicine 2006;25:13-21.
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Author
Oysu C, Topak M, Celik O, Yilmaz HB, et al.
Title
Effects of the acute exposure to the electromagnetic field of mobile phones on human auditory brainstem responses.
Journal
Eur Arch Otorhinolaryngol 2005 Feb 25 (Epub ahead of print).
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Author
Ozturan O, Erdem T, Miman MC, Kalcioglu MT, et al.
Title
Effects of the electromagnetic field of mobile telephones on hearing
Journal
Acta Otolaryngol 2002;122:289-293.
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Authors
Panda NK, Jain R, Bakshi J, Munjal S.
Title
Audiologic disturbances in long-term mobile phone users.
Journal
J Otolaryngol Head Neck Surg. (2010). 39(1):5-11.

Authors
Parazzini M, Bell S, Thuroczy G, Molnar F, et al.  
Title
Influence on the mechanisms of generation of distortion product otoacoustic emissions of mobile phone exposure.
Journal
Hear Res 2005;208:68-78.
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Authors
Parazzini M, Brazzale AR, Paglialonga P, Tognola G, et al.
Title
Effects of GSM cellular phones on human hearing: The European project “GUARD”.
Journal
Radiat Res 2007;168:608-613.
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Authors
Parazzini M, Sibella F, Lutman ME, Mishra S, Moulin A, Sliwinska-Kowalska M, Woznicka E, Politanski P, Zmyslony M, Thuroczy G, Molnár F, Kubinyi G, Tavartkiladze G, Bronyakin S, Uloziene I, Uloza V, Gradauskiene E, Ravazzani P.
Title
Effects of UMTS cellular phones on human hearing: Results of the European project “EMFnEAR”.
Journal
Radiat Res. (2009). 172(2):244-251.

Authors
Parazzini M, Lutman ME, Moulin A, Barnel C, Sliwinska-Kowalska M, Zmyslony M, Hernadi I, Stefanics G, Thuroczy G, Ravazzani P.
Title
Absence of Short-Term Effects of UMTS Exposure on the Human Auditory System.
Journal
Rad Research. Nov 18 2009 Ahead of print.

Author
Pau HW, Sievert U, Eggert S, Wild W.
Title
Can electromagnetic fields emitted by mobile phones stimulate the vestibular organ?
Journal
Otolaryngol Head Neck Surg 2005;132:43-9.
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Author
Sievert U, Eggert S, Pau HW.
Title
Can mobile phone emissions affect auditory functions of cochlea or brain stem?
Journal
Otolaryngol Head Neck Surg 2005;132:451-5.
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Author
Uloziene I, Uloza V, Gradauskiene E, Saferis V.
Title
Assessment of potential effects of the electromagnetic fields of mobile phones on hearing.
Journal
BMC Public Health 2005;5:39
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