An earplug is a device that is meant to be inserted in the ear canal to protect the user's ears from loud noises or the intrusion of water, foreign bodies, dust or excessive wind.
Protection from water 
Some earplugs are primarily designed to keep water out of the ear canal, especially during swimming and water sports. This type of earplug may be made of wax or moldable silicone which is custom-fitted to the ear canal by the wearer.
Exostosis, or Surfer's ear, is a condition which affects people who spend large amounts of time in water in cold climates. In addition, wind may increase the prevalence of the amount of exostosis seen in one ear versus the other dependent on the direction it originates from and the orientation of the individual to the wind. Custom-fitted surfer's earplugs help reduce the amount of cold water and wind that is allowed to enter the external ear canal and, thus, help slow the progression of exostosis.
A 2003 study published in Clinical Otolaryngology found that a cotton ball saturated with petroleum jelly was more effective at keeping water out of the ear, was easier to use, and was more comfortable than wax plugs, foam plugs, EarGuard, or Aquafit.
Jacques-Yves Cousteau, warned that earplugs are harmful to divers, especially scuba divers. Scuba divers breathe compressed air or other gas mixtures at a pressure matching the water pressure. This pressure is also inside the ear, but not between the eardrum and the earplug, so the pressure behind the eardrum will often burst the eardrum. Skin divers have less pressure inside the ears, but they also have only atmospheric pressure in the outer ear canal. "Doc's Proplugs" offer vented earplugs to allow divers to safely equalize and protect their ears. The PADI (Professional Association of Diving Instructors) advises in the "Open Water Diver Manual" that only vented earplugs designed for diving should be used in diving.
Hearing protection 
There are mainly three types of earplugs for hearing protection:
- Foam earplugs, mainly made of memory foam, which are compressed and put into the ear canal, where they expand to plug it.
- Silicone earplugs, which are rolled into a ball and carefully molded to fit over the external portion of the ear canal, providing a snug custom fit for the user.
- Flanged earplugs, including most types of musicians' or 'Hi-Fi' earplugs, as well as custom molds once they are molded.
NIOSH Mining Safety and Health Research recommends using the roll, pull, and hold method when using memory foam earplugs. The process involves the user rolling the earplug into a thin rod, pulling back on the ear, and holding the earplug deep in the canal with the finger. To get a complete seal, the user must wait about 20 seconds for the earplug to expand inside the canal.
Furthermore, they may be either disposable or non-disposable, with foam and silicone ones generally being disposable or for use a relatively limited number of times, while solid ones generally may be regarded as non-disposable. A variation of the traditional foam earplug is the no-roll foam earplug that uses a built-in central stem to push the foam plugs into the ears. These earplugs achieve a seal due to their tapered shape, rather than expansion after being rolled.
Ear plugs are especially useful to people exposed to excessively noisy devices or environments (80 dB or more).
|Level of noise in dB(A)||Maximum daily exposure time|
The first recorded mention of the use of wax earplugs is in the Odyssey, wherein Odysseus's crew used wax earplugs to avoid being distracted by the Sirens' songs. In 1907, the German company Ohropax, which produced earplugs, was started by German inventor Max Negwer. Current earplug material was discovered in 1967, at National Research in the USA by Ross Gardner and his team. As part of a project on sealing joints, they developed a resin with energy absorption properties. This E-A-R material was later developed into commercial memory foam earplugs.
'Basic' type plugs 
This kind of earplug protection is often worn by industrial workers who work within hearing distance of loud machinery for long periods, and is used by the British Ministry of Defense (MoD) for soldiers to use when firing weapons. Earplugs are rated for their ability to reduce noise. In the United States, the U.S. Environmental Protection Agency mandates that hearing protection be tested to provide a Noise Reduction Rating (NRR) where a panel of ten subjects are tested in a laboratory to determine the attenuation over a range of frequencies. In the European Union, hearing protectors are required to be tested according to the International Organization for Standardization (ISO) acoustical testing standard, ISO 4869 Part 1  and the Single Number Rating (SNR) or High/Middle/Low (HML) ratings are calculated according to ISO 4869 Part 2. In Brazil, hearing protectors are tested according to the American National Standards Institute ANSI S12.6-1997 and are rated using the Noise Reduction Rating Subject Fit NRR(SF). Australia and New Zealand have different standards for protector ratings yielding a quantity SLC80 (Sound Level Class for the 80th percentile). Canada implements a class system for rating the performance of protectors. Gauger and Berger have reviewed the merits of several different rating methods and developed a rating system that is the basis of a new American National Standard, ANSI S12.68-2007 
The various methods have slightly different interpretations, however, each method has an effective percentile associated with the rating for which that percent of the users should be able to achieve the rated attenuation. For instance the NRR is determined by the mean attenuation minus two standard deviations, thus it translates to a 98% statistic. That is at least 98 percent of users should be able to achieve that level of attenuation. The SNR and HML are a mean minus one standard deviation statistic. Therefore, approximately 86% of the users should be able to achieve that level of protection. Similarly, the NRR(SF) is a mean minus one standard deviation and represents an 86% of users should achieve that level of protection. The difference between the ratings lies in how the protectors are tested. NRR is tested with an experimenter-fit protocol. SNR/HML are tested with an experienced subject-fit protocol. NRR(SF) is tested with a naive subject-fit protocol. According to Murphy et al. (2004), these three protocols will yield different amounts of attenuation with the NRR being the greatest and NRR(SF) being the least.
The experimenter-fit NRR should be adjusted per the guidelines of the National Institute for Occupational Safety and Health as the required NRR ratings differ greatly from lab tests to field tests.
To compensate for known differences between laboratory-derived attenuation values and the protection obtrained by a worker in the real world, the labeled noise reduction ratings shall be derated as follows: (1) earmuffs- subtract 25 % from the manufacturers' labeled NRR; (2) slow-recovery formable earplugs subtract 50%; and (3) all other earplugs - subtract 70% from the manufacturers labeled NRR. These derating values shall be used until such time as manufacturers test and label their products in accordance with a subject-fit method such as Method B of ANSI S12.6-1997.
— NIOSH, Criteria for a Recommended Standard: Occupational Noise Exposure, DHHS (NIOSH) Publication No. 98-126
The NRR(SF) used in Brazil does not require derating as it resembles the manner in which the typical user will wear hearing protection.
Most earplugs are elastic ones made of memory foam, that is typically rolled into a tightly compressed cylinder (without creases) by the user's fingers and then inserted in the ear canal. Once released, the earplug expands until it seals the canal, blocking the sound vibrations that could reach the eardrum. Other plugs simply push into the ear canal without being rolled first. Sometimes earplugs are connected with a cord to keep them together when not in use. Other common material bases for earplugs are viscous wax or silicone.
Other devices that provide hearing protection include electronic devices worn around and/or in the ear, designed to cancel out the loud noise of a gunshot, while possibly amplifying quieter sounds to normal levels. While rich in features, these electronic devices carry a price over one hundred times that of their foam counterparts.
Noise reduction ratings 
Hearing protectors sold in the U.S. are required by the U.S. Environmental Protection Agency (EPA) to have a noise reduction rating (NRR), which is an estimate of the reduction of noise at the ear when protectors are worn properly. However, due to the discrepancy between how protectors are fit in the testing laboratory and how users wear protectors in the real world, the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) have developed derating formulas to reduce the effective NRR.
While the NRR and the SNR (Single Number Rating) are designed to be used with C-weighted noise, which means that the lower frequencies are not de-emphasized, other ratings (NRR(SF) and NRSA) are determined for use with A-weighted noise levels, which have lower frequencies de-emphasized. The National Institute for Occupational Safety and Health recommended and the U.S. EPA mandated  that 7-dB compensation between C and A weighting be applied when the NRR is used with A-weighted noise levels.
OSHA has defined in their training manual for inspectors that the adequacy of hearing protection for use in a hazardous noise environment should be derated to account for how workers typically wear protection relative to how manufacturers test the protector's attenuation in the laboratory. For all types of hearing protection, OSHA’s derating factor is 50%. If used with C-weighted noise, the derated NRR will become NRR/2. If used with A-weighted noise, OSHA applies the 7-dB adjustment for C-A weighting first then derates the remainder. For example, a protector with 33-dB attenuation would have this derating:
- Derated NRR = (33 – 7)/2
NIOSH has proposed a different method for derating based upon the type of protector. For earmuffs, the NRR should be derated by 25%, for slow-recovery foam earplugs the derating is 50% for all other protection, the derating is 70%. NIOSH applies the C-A spectral compensation differently than OSHA. Where OSHA subtracts the 7-dB factor first and derates the result, NIOSH derates the NRR first and then compensates for the C-A difference. For example, to find the derated NRR for an earmuff by using the NIOSH derating system, the following equation would be used:
- Derated NRR = (Original NRR x (1-.25)) – 7
Expected updates 
In 2007, the American National Standards Institute published a new standard for noise reduction ratings for hearing protectors, ANSI S12.68-2007. Using the real ear attenuation at threshold data collected by a laboratory test prescribed in ANSI S12.6-2008, the noise reduction statistic for A-weighted noise (NRSA) is computed using a set of 100 noises listed in the standard. The noise reduction rating, rather than be computed for a single noise spectrum the NRSA incorporates variability of both subject and spectral effects. ANSI S12.68 also defines a method to estimate the performance of a protector in an atypical noise environment. Building upon work from the U.S. Air Force and the ISO 4869-2 standard, the protector's attenuation as a function of the difference in C and A-weighted noise level is used to predict typical performance in that noise environment. The derating may be quite severe (10 to 15 decibels) for protectors that have significant differences between low and high frequency attenuation. For "flat" attenuation protectors, the effect of C-A is less. This new system eliminates the need for calculators, relies on graphs and databases of empirical data, and is believed to be a more accurate system for determining NRRs.
Musicians' or 'Hi-Fi' earplugs 
Musicians who perform music styles noted for their loud nature, especially rock music, often wear earplugs to prevent their own performances from damaging their hearing. Musicians' earplugs are designed to attenuate sounds evenly across the audio band and thus minimise their effect on the user's perception of bass and treble levels. These are commonly used by musicians and technicians, both in the studio and in concert, to avoid overexposure to high volume levels. Alternately, musicians may use in-ear monitors, which are essentially headphones that also serve as earplugs.
They generally achieve this by incorporating a tiny diaphragm to reduce low frequencies, together with absorbent or damping material for high frequencies. This means they can be quite costly, being intended for constant re-use unlike simple earplugs which are disposable. These earplugs usually give an attenuation of only about 20dB and are not intended for protection from very high noise levels (beyond 105 dB).
Some musicians' earplugs are custom-made for the individual listener. An audiologist administers a hearing test and makes molds of the ear. A company then makes a custom ear-piece into which different attenuator capsules can be inserted. These different capsules will provide different levels of attenuation, usually 9, 15, and 25 dB. These types of earplugs will provide the flattest attenuation and the truest isolation from outside noise, as they fit firmly into the individual's ears. They also provide much better protection from very high noise levels. This type of plug is quite popular amongst audio engineers who can safely listen to loud mixes for extended periods of time.
Electronic earplugs 
The noise reduction of passive earplugs varies with frequency but is independent of value (soft noises are reduced as much as loud noises). As a result, while loud noises are softened, protecting hearing, it is difficult to hear soft noises. Active electronic earplugs exist, where loud noises are reduced more than soft noises, and soft sounds may even be amplified, providing dynamic range compression. This is done by having a standard passive earplug, together with a microphone/speaker pair (microphone on outside, speaker on inside; formally a pair of transducers), so sound can be transmitted without being attenuated by the earplug. This protects hearing, but allows one to hear normally when sounds are in safe ranges – for example, have a normal conversation when there are no noises, but be protected from sudden loud noises, or hear soft passages in music but be protected from sudden sounds like cymbal crashes.
Flight ear protection 
Earplugs are available which help to protect ears from the pain caused by airplane cabin pressure changes. Some products contain a porous ceramic insert which reportedly aids equalization of air pressure between the middle and outer ear thereby preventing pain during landings and take-offs. Some airlines distribute regular foam earplugs as part of their amenity kits for passengers to aid their comfort during landings and takeoffs as well as to reduce exposure to the aircraft's noise during the flight. These can help passengers get to sleep during the flight if desired.
Earplugs for sleeping are made to be as comfortable as possible while blocking external sounds that may prevent or disrupt sleep. Specialized earplugs for such noises as a partner's snoring may have sound-dampening enhancements that enable the user to still hear other noises, such as an alarm clock.
To determine the comfort of earplugs used for sleeping, it is important to try them on while actually lying down. The pressure on the ear between the head and pillow may cause significant discomfort. Furthermore, just tilting the head back or to the side causes significant anatomical changes in the ear canal, mostly a reduction of the ear canal diameter, which may reduce comfort if the earplug is too large.
Health risks 
Earplugs are generally safe, but some precautions may be needed against a number of possible health risks, with additional ones appearing with long term use:
- Pushing in earplugs into the external ear canal may cause the air pressure to rise in it, in effect pushing against the eardrum and causing pain. This may be caused by pressure on the ear while lying down on the side, and is also the case when completely expanded foam earplugs are pushed further into the ear. To bypass the latter risk, such earplugs are instead removed, compressed and inserted to the desired depth. Vice versa, when pulled out, the resultant negative pressure pulls the eardrum. Therefore, some earplugs are better carefully screwed or jiggled out rather than yanked out. Yawning does not help to equalize this air pressure difference, since it equalizes the pressures between the middle ear and the environment, while this overpressure rather is located in the outer ear, between the eardrum and the earplug.
- If pushed too far into the ear canal, they may push earwax and debris into the canal and possibly against the ear drum. As a precaution, ear plugs should not be pushed further into the ear canal than they may be grabbed and rotated. Earwax impacted by earplugs can be removed by irrigation or other remedies, as described here.
- There is a possibility for allergic reactions, but this is likely rare, as earplugs generally are made of immunologically inert materials.
Long-term use 
Custom shaped plugs are recommended for long-term use, since they are more comfortable and gentle to the skin and won't go too far into the ear canal.
Nevertheless, prolonged or frequently repeated use of ear plugs have the following health risks, in addition to the short term health risks:
- They may cause earwax to build up and plug the outer ear, since it blocks the normal flow of earwax outwards. This can result in tinnitus, hearing loss, discharge, pain or infection. Excess earwax should be carefully removed from the ear, and earplugs should be cleaned regularly with water and mild soap. However, foam type ear plugs are usually designed to be disposable, and will expand and lose their memory property upon drying after washing with water and soap. They will become quite spongy, expand very quickly after being compressed, making them quite problematic in proper insertion into the ear canal. They also lose a large proportion of sound attenuating capability after such washing and drying.
- They may cause irritation of the temporomandibular joint, which is located very close to the ear canal, causing pain. Individually fitted non-elastic earplugs may be less likely to cause this irritation compared with foam ones that expand inside the ear canal.
- Earplugs are also a possible cause of ear inflammation (otitis externa), although the short term use of earplugs when swimming and shampooing hair may actually help prevent it. Still, many pathogenic bacteria grow well on warm, moist, foam-type plugs (polyvinylchloride (PVC) or polyurethane). However, there need also be a loss of integrity of the skin for infection to occur. Hard and poorly fitting ear plugs can scratch the skin of the ear canal and set off an episode. When earplugs are used during an acute episode, disposable plugs are recommended, or used plugs must be cleaned and dried properly to avoid contaminating the healing ear canal with infected discharge.
Custom molds 
Noise and decibel reduction earplugs can be molded to fit an individual's ear canal. This is associated with a higher cost, but can help to reduce the discomfort typically experienced after longer use, or if the level of protection or performance is inadequate.
Pressure and flight earplug molds are less common, as they are typically not used as long as other earplugs, and are therefore less in demand.
For best results they are molded in the ear while in the position that they will be used. For instance, if they are to be used for sleeping then they should be molded in the ear while lying down, as different positioning of the jaws causes significant changes to the form of the ear canal, mostly a reduction of the diameter, risking the sleep earplug to be made too large otherwise. These changes can be felt by feeling with a finger just at the entrance to the ear canal while moving the jaws sideways, up and down or anterior and posterior.
Most moulded earplugs are made from silicone but other materials may be used, including thermoplastics.
See also 
- King, John F.; et al. (2010). "Laterality of Exostosis in Surfers Due to Evaporative Cooling Effect". Otology & Neurotology 31 (2): 345–351. doi:10.1097/MAO.0b013e3181be6b2d. PMID 19806064.
- Chisholm, E.J.; Kuchai, R.; McPartlin, D. (2004). "An objective evaluation of the waterproofing qualities, ease of insertion and comfort of commonly available earplugs". Clinical Otolaryngology and Allied Sciences 29 (2): 128–32. doi:10.1111/j.1365-2273.2004.00795.x. PMID 15113295.
- The Silent World (New York:1953, Harper, pp. 5-6)
- "How To Wear Soft Foam Earplugs." NIOSH Mining Safety and Health
- U.S. Environmental Protection Agency Code of Federal Regulations 40 CFR 211 Subpart B
- ISO 4869-1 (1990). Acoustics—Hearing Protectors Part 1: Subjective method for the measurement of sound attenuation, International Organization for Standardization, Geneva.
- ISO 4869-2 (1994). Acoustics—Hearing Protectors Part 2: Estimation of effective A-weighted sound pressure levels when hearing protectors are worn, International Organization for Standardization, Geneva.
- ANSI S12.6-1997 [R2002] (2002) American National Standard for the Measuring Real-Ear Attenuation of Hearing Protectors, American National Standards Institute, New York.
- Gauger, D., and Berger, E. H. (2004). A new hearing protector rating: The noise reduction statistic for use with A-weighting (NRSA), Technical Report No. E-A-R 04-01/HP, American National Standards Institute, New York. This report can be found online at the following URL web URL http://www.e-a-r.com/pdf/hearingcons/TO4_01EPA.pdf.
- ANSI S12.68 (2007). American National Standard Methods of Estimating Effective A-Weighted Sound Pressure Levels When Hearing Protectors, are Worn, American National Standards Institute, New York.
- Murphy, William J.; Franks, John R.; Berger, Elliott H.; Behar, Alberto; Casali, John G.; Dixon-Ernst, Christine; Krieg, Edward F.; Mozo, Ben T. et al. (2004). "Development of a new standard laboratory protocol for estimation of the field attenuation of hearing protection devices: Sample size necessary to provide acceptable reproducibility". The Journal of the Acoustical Society of America 115 (1): 311–23. doi:10.1121/1.1633559. PMID 14759024.
- National Institute for Occupational Safety and Health, June 1998, Criteria for a Recommended Standard: Occupational Noise Exposure, NIOSH Publication, No. 98-126
- EPA Standard, Title 20, Part 211
- Occupational Health and Safety Administration, January, 1999. The OSHA Technical Manual, OSHA Publication, Section IV, Appendix IV: C.
- Alpine - Sleepsoft ear plugs
- http://blog.allearplugs.com/blog/2010/9/8/the-right-size-ear-plug.html – The right size ear plug (access date 2010-09-08)
- "Can earplugs be harmful?", Netdoctor.co.uk
-  Webbikeworld.com
- Columbia University - Ear plugs
- ZenPlugs Custom Moulded Earplugs
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