Noise and noise unhealthiness

What is noise?
~ a sound, especially one that is loud or unpleasant or that causes disturbance.

Just like air, water or plastic pollution, there also exists noise pollution. The human ear and lower auditory system continuously receive stimuli from the world around us. This doesn’t mean all the acoustical inputs are necessarily disturbing or have harmful effects on the human body. This is because the auditory nerve provides activating impulses to the brain that enable us to regulate the vigilance necessary for optimal performance. On the other hand there are even scientific reports, that a completely silent world can have harmful effects, because of sensory deprivation. Thus, any sound can be damaging, regardless of its intensity.

What we consider as noisy is influenced by subjective factors, such as our mood, the time of day and objective factors like the background noise level, type of noise (see table), the frequency of noise or how long we are exposed to it. At one extreme there are the tinny sounds coming from the headphones of somebody listening to a portable audio player that drive us crazy; at the other extreme the sound of a jet engine at close quarters can cause irreversible hearing damage. Other noisy sources would be: railway traffic, motor vehicles, manufacturing plants or simply a baby crying or doors being slammed. Noise from airports or sudden impulse noises are typically perceived as more bothersome than noise from traffic of equal volume.

Sound is characterized by 2 quantities: acoustic pressure (in Pa) and frequency (in Hz). Noise is measured by sound pressure level which is expressed as a power ratio and calibrated in decibels (dB). For more information:

The WHO guidelines for community noise recommend less than 30dB in bedrooms during the night for a sleep of good quality and less than 35dB in classrooms to allow good teaching and learning conditions. They also recommend less than 40dB of annual average night noise outside of bedrooms.

Why is noise unhealthy? Biological effects…
Noise represents an important public health problem, because it can lead to different health problems: Hearing impairment can begin at around 85 dB. It’s even possible to die when exposed to sounds over 200 dB, because the alveoli are bursting.
 * Hearing impairment
 * Interference with spoken communication
 * Sleep disturbances
 * Cardiovascular diseases
 * Disturbances in mental health
 * Impaired task performance
 * Negative social behaviour and annoyance reactions

Some groups are more vulnerable to noise. As children spend more time in bed than adults, they are more exposed to night noise. Pregnant women, chronically ill and elderly people are more sensitive to disturbance. Shift workers are at increased risk because their sleep structure is under stress.

...on the ear
Mechanical damage to the ear may occur after repeated noise expose or acute high intensity damaging. This is then called noise-induced hearing loss (NIHL). It’s also important to note, that high noise level in a short amount of time has the same damaging effect like low noise level over a long period of time.

Prolonged exposure makes blood vessels in the ear constrict, which leads to a lack of oxygen. Stereocilia of inner and outer hair cells of the cochlea then become fused and bent or break. A very loud sound in a particular frequency range can damage the cochlea's hair cells that respond to that range, thereby reducing the ear's ability to hear those frequencies in the future. Very loud noise like explosions, that cover a large frequency range, have harmful effects across the entire range of human hearing and can even lead to injuries of eardrum and displacement of auditory ossicles. Once lost, hearing cannot be restored in humans.

Presbycusis is the age-related hearing-loss. The cause is the decreased flexibility of eardrum, auditory ossicles, etc. and fusing and breaking of stereocilia.

...on the body
Acute noise exposures activate the autonomic and hormonal systems, leading to temporary changes in organ systems. Depending on quality, quantity and time of exposure as well as mental and physiological condition of the person, different changes in the organism occur, for example:
 * increased adrenalin and noradrenalin concentration > increased blood pressure and heart rate, vasoconstriction
 * shifts in electrolyte balance, blood viscosity
 * changes in behaviour
 * increased blood glucose level

Prevention and Protection
Prevention and raising awareness about the dangers of noise in general is paramount, as there are no treatments for curing hearing loss. This includes:
 * 1) Lowering the volume of sound at its source
 * 2) More distance from the source (sound intensity follows an inverse square: doubling the distance from a noise source reduces its intensity by a factor of four)
 * 3) Limiting the time of exposure
 * 4) Physical protection (barriers, sound absorbent materials, appropriate home design)

New studies reveal…
It is believed exposure to low frequency sound vibrations (infrasound), which can't be picked up by the human ear, may also have considerable impact on humans. The problem of infrasound is, that it can carry through the atmosphere for thousands of kilometres. This is a very important point in the discussion about wind turbines as their have a very strong effect on their surroundings. The blade tips of a wind turbine can spin at speeds of up to 80 meters per second. In high winds, this rapid spinning can produce low-frequency sound and vibration, in addition to disruptions in air pressure. One study has suggested that infrasound may cause feelings of fear and disorientationin humans as well as hallucination and is believed to cause certain breathing and digestive problems.

Books
Ekbert Hering, Rolf Martin, Martin Stohrer; Physik für Ingenieure; 3. edition; 1989; ISNB 3-18-400916-5

Frantisek Vítek; Lectures on biophysics with medical orientation; (edition not given); 2011; ISBN 978-80-246-2006-0

Webpages
WHO; http://www.who.int/docstore/peh/noise/guidelines2.html; last access: 14.11.2015

DUDEN Lernhelfer; https://www.lernhelfer.de/schuelerlexikon/biologie/artikel/laerm; last access: 17.11.2015

Lars Jarup; Marie-Louise Dudley; et al.; http://www.medscape.com/viewarticle/516462; last access: 17.11.2015