Close to 40 million American adults have hearing loss, making it one of the most common health concerns people face, according to the NIH.

While most causes of hearing loss are well-understood, researchers are still studying all the possible causes, methods for prevention and treatment options. In some cases, no cause can be determined.

The most common type of hearing loss is known as age-related hearing loss, or presbycusis. This means the gradual loss of hearing that occurs over time. As with other body changes related to aging, hearing loss is a normal—but treatable—part of aging. You may not realize it’s happening until your symptoms become severe or someone else notices you’re having trouble.

This type of loss is permanent and usually makes it harder to hear what are known as "high-frequency" sounds, such as children's voices, birds chirping or the ringing of a telephone. 

The main symptoms that indicate you may have age-related hearing loss? First, you may feel like you can hear, but not understand. You may find certain sounds annoying or too loud. You also may notice more episodes of tinnitus (ringing in the ears).

Presbycusis is a type of sensorineural hearing loss, which means it occurs from changes in the inner ear as a person ages. It also can be the result of changes in the middle ear, or along the nerve pathways leading to the brain. As you age, heart-related conditions like high blood pressure also affect how well you hear.  

Hereditary hearing loss can be conductive, sensorineural or mixed and is sometimes the result of a genetic trait passed down from a parent. There are more than 400 known genetic and rare syndromes that include hearing loss. It's likely more will be identified as genetic testing becomes even more sophisticated. 

The degree of loss can vary widely from person to person, even those with the same genetic condition. For some people, hearing aids will be sufficient. For others, cochlear implants and/or learning American Sign Language will be recommended. 

While many hereditary hearing losses are congenital (present at birth), some of these conditions develop slowly over time.

Noise-induced hearing loss is caused by prolonged exposure to loud noise. The culmination of constant exposure to every day sounds like traffic, construction work, noisy office environments or loud music can negatively impact your hearing. While noise-induced hearing loss is generally temporary in nature, repeated overexposure to loud noise makes it harder for the ears to recover between events. The noise damages inner ear hair cells, causing hearing loss to deteriorate over time and become permanent.

Remember: Noise-induced hearing loss is largely preventable.

You can significantly lower your risk of hearing loss by limiting exposure to loud noises, using earplugs in noisy environments, and using your headphones wisely.

There are numerous illnesses, autoimmune diseases and conditions that contribute to hearing loss, including:

More: Seven surprising causes of hearing loss

Unilateral hearing loss (UHL), sometimes referred to as single sided deafness (SSD), is hearing loss that occurs in just one ear. It can cause difficulty hearing speech on the affected side and locating the source of sounds.

Causes of unilateral hearing loss include:

Sudden hearing loss should be evaluated promptly by an otolaryngologist or other physician—the faster the treatment, the better the chance of recovery. If it is due to a cause that is not medically treatable, specialized hearing aids called CROS (Contralateral Routing of Signal) aids or bone-anchored hearing aids can be considered.

There are numerous drugs and medications linked to hearing loss, known as ototoxic drugs. These include:

Generally, you must take large and prolonged doses of these types of drugs to notice effects of hearing loss, but research is still being conducted to further understand the effects of specific dosages and medications.

Another cause for hearing loss is from tumors such as an acoustic neuroma. Tumor-related hearing loss might also include tinnitus (ringing in the ears), or you might have a sensation of fullness in one or both ears. Tumors are usually treated either medically or surgically and normal hearing may or may not be restored.

Head trauma can damage inner ear structures causing a temporary or permanent hearing loss. Any injury sustained to the head should be evaluated by a doctor immediately. The medical evaluation will likely include both a hearing and eye examination.

There are so many potential causes of hearing loss. Hearing healthcare professionals are trained to use many diagnostic tests to help get to the bottom of your concerns. Once they determine the cause, they can find the best course of treatment. If you have hearing loss and are unsure of the cause, visit a qualified clinic near you from our consumer-reviewed directory.