Age may also be a significant factor. Some psychoactive drugs such as LSD, methaqualone, or phencyclidine can cause hyperacusis. An antibiotic, ciprofloxacin, has also been seen to be a cause, known as ciprofloxacin-related hyperacusis. Benzodiazepine withdrawal syndrome is also a possible cause. Neurophysiological mechanisms
As one important mechanism, adaptation processes in the auditory brain that influence the dynamic range of neural responses, are assumed to be distorted by irregular input from the inner ear. This is mainly caused by hearing loss related damage in the inner ear. The mechanism behind hyperacusis is not currently known, but it is suspected to be caused by damage to the inner ear and cochlea. It is theorized that type II afferent fibers become excited after damage to hair cells and synapses, triggering  a release of ATP in response. This release of ATP results in pain, sound sensitivity, and cochlear inflammation. Diagnosis
The basic diagnostic test is similar to a normal audiogram. The difference is that additionally to the hearing threshold at each test frequency also the lowest uncomfortable sound level is measured. This level is called loudness discomfort level (LDL), uncomfortable listening level (UCL), or uncomfortable loudness level (ULL). In patients with hyperacusis this level is considerably lower than in normal subjects, and usually across most parts of the auditory spectrum.
Sensitivity is often different between ears. Noxacusis (Pain Hyperacusis)
In some instances, hyperacusis is accompanied by pain, which is known as noxacusis. Noxacusis is characterized by pain resulting from sounds, often initiated at certain volumes or frequencies; pain can be immediate or delayed, and sometimes persists for an extended period of time following exposure. Pain can be acute or chronic, and is often described as stabbing, burning, acid, or nerve pain, and is sometimes equated with the pain of a root canal or a broken tooth. Loudness Discomfort Level (LDL)
The threshold of sound at which discomfort is initially experienced; measured in decibels (dB). Setback
After a period of some relief from symptoms, discomfort resumes; often resulting from exposure to sound, or, in some cases, ototoxic medications or injuries. Setback prevention is an important focus among those affected. Associated conditions
Some conditions that are associated with hyperacusis include:

Causes
The most common cause of hyperacusis is overexposure to excessively high decibel (sound pressure) levels.Some affected people acquire hyperacusis suddenly as a result of taking ear sensitizing drugs, Lyme disease, Ménières disease, head injury, or surgery. Others are born with sound sensitivity, develop superior canal dehiscence syndrome, have had a history of ear infections, or come from a family that has had hearing problems. Bells palsy can trigger hyperacusis if the associated flaccid paralysis affects the tensor tympani, and stapedius, two small muscles of the middle ear. Paralysis of the stapedius muscle prevents its function in dampening the oscillations of the ossicles, causing sound to be abnormally loud on the affected side.