Causes and Risk Factors of Middle Ear Infection

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While children are at the greatest risk of middle ear infections (also called otitis media), adults can also experience them. Blockage of the eustachian tube is the usual cause, as it allows a bacterial or viral infection to develop in the middle ear. The blockage can be triggered by colds, allergies, and other respiratory infections, and children's eustachian tubes are more prone to blockage from fluid or inflammation.

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Common Causes

The most common cause of otitis media is eustachian tube blockage. The eustachian tube is a passageway from the back of your nose and throat to your middle ear, which is the part of your ear that is behind the eardrum. Your eustachian tube regulates air pressure in the middle ear and drains secretions.

Eustachian Tube Blockage

If the eustachian tube is blocked, fluid or bacteria can become trapped inside the ear and cause an infection.

Eustachian tube dysfunction is more common in children because it doesn't drain as well as adults—the passage is narrower and doesn't slant as much as it does in adults. For some, inadequate drainage can persist into adulthood and is the main cause of middle ear infections in adults.

Adenoids, located in the back of the nose near the opening of the eustachian tubes, can block the tubes if they become swollen or inflamed. This is more of a problem in children because their adenoids are relatively larger.

Infectious Organisms

Both bacteria and viruses can produce an ear infection if they get trapped in the middle ear.

  • The most common bacteria that cause ear infections are Streptococcus pneumoniae and Haemophilus influenzae, with less common infections owed to Streptococcus pyogenes and Staphylococcus aureus.
  • Viruses that cause ear infections include cold viruses (rhinoviruses), respiratory syncytial virus (RSV), influenza virus, and enteroviruses.

Standard childhood vaccinations protect against some of these infections and help prevent ear infections.

Common Risk Factors


Babies and toddlers between the ages of 6 months and 2 years are at the greatest risk for ear infections. This is because of the structure of their eustachian tube and the fact that their immune systems are still developing.

Risk factors for blocked eustachian tubes and middle ear infections include:

  • Upper respiratory tract infections (URIs): Children are more at risk of catching colds because their immune systems have had less exposure to viruses (and, therefore, haven't developed defenses against them). That said, URIs are also a risk factor for adults.
  • Allergic rhinitis: Seasonal hay fever, allergies to specific allergens, or chronic allergies can predispose to ear infections in both children and adults. Allergies cause more secretions, and the inflammatory compounds released also irritate and damage the lining of the ears. Controlling allergies can help reduce the risk. However, antihistamines and decongestants have not been found to be of benefit in preventing otitis media in children.
  • Malformation of the eustachian tube or craniofacial (head/face) disorders that cause palatal muscle weakness like cleft palate
  • Mucosal disease of the ears, nose, or throat, such as sinusitis
  • Enlarged structures in your ears, nose, or throat like the adenoids, turbinates, or nasal polyps. Very rarely a tumor can block the eustachian tube.
  • A weakened immune system
  • A family history of susceptibility to ear infections


Like many infections, not receiving treatment for a middle ear infection can result in complications, including hearing loss. Hearing loss can occur in any age group, and it causes delays in speech and language development for children.

There is also the risk of the infection spreading to the mastoid bone and other tissues. Seeking care from your doctor and following treatment recommendations can help you cope with the symptoms and avoid these complications.

Lifestyle Risk Factors

Smoking or exposure to secondhand smoke can increase the likelihood of ear infections, especially for children. Not staying updated on recommended vaccines or not paying attention to avoiding contagious infections can increase the risk as well.

Placing objects in the ear, such as q tips, especially if you reuse them, can expose your ears o infectious viruses or bacteria.

Babies and Children

  • If you choose to breastfeed, consider doing so for at least six months so your baby benefits from the antibodies in your breast milk.
  • Keep your baby in an upright position when bottle feeding. Don't prop up a bottle while your child is lying flat.
  • Reduce the use of a pacifier once your baby is 6 months old, as some studies have found this increases the risk of ear infections.
  • Avoid exposing babies and children to cigarette smoke; it impairs the function of the eustachian tubes and increases the risk of middle ear infections.
  • Get the Prevnar 13 vaccine, which protects against ear infections by 13 subtypes of Streptococcus bacteria, and the annual flu shot.
  • Leave any removal of earwax to a pediatrician. Cotton swabs and other objects can clog and irritate ear canals, leading to infection.

Adults

  • Stop smoking and avoid secondhand cigarette smoke.
  • Take a decongestant when you have a cold or before getting on an airplane so your eustachian tubes are less likely to become congested when you experience a change in air pressure during ascent and descent.
  • Avoid trying to clean your earwax using cotton swabs or other objects.

Frequently Asked Questions

Why do babies get ear infections?

Babies and toddlers are especially prone to ear infections because their Eustachian tubes are short, narrow, and more horizontal than vertical, which makes the drainage less efficient and makes it easier for bacteria and viruses to get trapped inside. Babies' adenoids (glands in the back of the throat) also are large enough to partially block the opening of the Eustachian tubes.

What fungus can cause ear infections?

Among the fungi known to cause fungal ear infections, also known as otomycosis or fungal otitis externa, are Aspergillus, Candida, and Pseudallescheria boydii. People with impaired immune systems are especially susceptible.

Do ear infections ever clear up without treatment?

Yes. In fact, most doctors opt not to treat ear infections beyond advising parents or patients to use over-the-counter pain medication to ease discomfort. This is true even of bacterial ear infections, as treating them with antibiotics is rarely necessary and can contribute to antibiotic resistance.

How can I protect my child from getting ear infections?

Measures you can take to help prevent your child from developig middle ear infections include:

  • Breastfeed.
  • Wash your hands, and your child's, frequently and thoroughly.
  • Keep them away from secondhand smoke.
  • Steer clear of people who are sick.
  • Make sure they're up-to-date on vaccinations.
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