/ Ear Infection
What Causes Ear Infections?

What Causes Ear Infections?

An infection is the invasion and reproduction of microorganisms that are foreign to the body. There are many microorganisms living within the body that are part of our natural human microbiota and are not considered infectious. Unfortunately occasional bacteria, viruses, fungi, or parasites that are unwanted do find their way into the body and reproduce – resulting in an infection.

Our bodies have a complex system of fighting infections known as the immune system. It is composed of natural barriers such as skin, mucous membranes, airways, digestive tract, urinary tract, and the vagina that either block or flush out invasive microorganisms. Other defenses include white blood cells, inflammation (as a way of signaling to the body that there is an infection), production of antibodies, and fever. Earwax contributes to the immune system thanks to its antibacterial properties and its ability to clean the ear canal by removing dead skin or other particles.

Causes of ear infections often relate to the ear canal or Eustachian tubes. But before getting too detailed with what causes ear infections, let’s review the anatomy of the ear to help understand what causes them. Your ears are made up of three main cavities: the Inner Ear, the Middle Ear and the Outer Ear. Each section has its own function and structure:

Outer Ear - The outer ear is made up of the pinna and the ear canal. The pinna is the part of the ear that we see on the outside of our heads. It is made up of cartilage and soft tissue and is responsible for collecting and guiding sound vibrations from the outside world into the ear canal, which is a 2 to 3 cm tube that propels sound to the eardrum. The ear canal is open to the outside world and depends on earwax to protect itself from foreign microorganisms.

Middle Ear - The middle ear is the air-filled space behind the eardrum. Within the middle ear there are three small bones, called ossicles. When sound waves hit the eardrum and cause it to move, the ossicles vibrate and subsequently cause fluid in the inner ear to vibrate. The middle ear is connected to the upper respiratory tract by the Eustachian tubes, which are a pair of narrow tubes that run from each middle ear to high in the back of the throat, behind the nasal passages. The tubes open and close at the throat end to:

  • Regulate air pressure in the middle ear
  • Refresh air in the ear
  • Drain normal secretions and debris from the middle ear

Inner Ear – The inner ear is comprised of three sections. Only one of which, a bony snail-shaped structure called a Cochlea, is involved with hearing. The Cochlea is filled with fluid and small hair-like nerve cells. The vibrations in the fluid are interpreted by the hair-like nerve cells, which send electrical signals to the auditory nerve, allowing us to hear. The other sections, the vestibule and semicircular canals, are involved with the sensations of equilibrium and balance.


Ear Infection Causes

What Causes Ear Infections in the Middle Ear?

Clogging of the Eustachian tubes is often what causes an ear infection in the middle ear. Should this occur, the middle ear can no longer drain fluids or moisture properly and it becomes a favorable environment for invasive microorganisms to multiply. The Eustachian tubes are less developed in young children and infants (more narrow and horizontal), which is what causes ear infections to be more common in children. Children in the age range of 3 months to 3 years are at heightened risk of developing an ear infection due to the susceptibility of their Eustachian tubes to blockage. Obstruction of the Eustachian tubes (possibly resulting in an ear infection) can result from the following:

  • Viral Infections – Of the causes of ear infections, the most common trigger is the common cold or flu. Other forms of upper respiratory infections can also cause swelling of the Eustachian tube, which affects the tube's ability to deliver regular airflow to the middle ear.
  • Allergies – Allergies to pollen, food, or animal dander can be one of the causes of ear infections. One symptom of these types of allergies is obstruction of the Eustachian tubes, similar to the common cold or flu. In some cases, exposure to smoke, fumes and various types of airborne toxins can cause swelling in the Eustachian tube and be what causes ear infections.
  • Bacteria - In rare circumstances where the immune system is lowered by other diseases, bacteria can be what causes an ear infection. In such cases, bacteria often attack the middle ear after a viral infection or an allergy. Bacteria can cause damage to the middle ear often triggering high fevers and hearing loss.

What Causes Ear Infections in the Outer Ear?

The outer ear is separated from the middle ear by a membrane commonly known as the eardrum. The causes of ear infections in the outer ear are unrelated to the middle ear, Eustachian tubes, or respiratory infections such as a cold or the flu. Most commonly, outer ear infections occur when water, sand, or other debris irritate the ear canal. Often this occurs after swimming, which is what causes ear infections of this sort to be colloquially termed "swimmer's ear". Swimming in dirty water with high bacteria counts is extra likely to result in an outer ear infection.

Bacteria are the most likely culprit of an outer ear infection, but fungal infections are possible and even more rarely, viral infections can occur here as well. Each type of microorganism tends to infect the ear canal through similar causes of ear infections.

  • Too much moisture in the ear – Bacteria like water. When excess water remains in your ear canal after swimming, showering, sweating, or from excessively humid weather; bacterial infections are more likely to occur.
  • Scratches, abrasions, or other irritations to the ear canal – The skin inside the ear canal is very sensitive and small perturbations can cause irritation or temporary damage. If that occurs, bacteria will be more likely to grow inside the ear canal. "Cleaning" earwax out of the ear using cotton swabs or hairpins is not recommended as it can cause irritation of the ear canal and be what causes ear infections. Furthermore, using cotton swabs is most likely to push earwax further into the ear canal causing blockage and reduced hearing. Other objects that irritate the ear canal and can be causes of ear infections include: fingers, headphones, hearing aids, and ear plugs. Do not use ear candles to clean out earwax, they can result in burns and other issues.
  • Sensitivity reactions – Other materials can irritate the ear canal such as hairspray and jewelry. Jewelry can be irritating for persons with eczema or allergies.

What Causes Ear Infections in the Inner Ear?

The inner ear, also known as the labyrinth, receives mechanical vibrations from the middle ear and translates them to electrical signals that are interpretable by the brain. The inner ear also provides balance for the body and a sense of equilibrium. It is less accessible to foreign microorganisms when compared to the middle and outer ear however, infections of the inner ear do unfortunately occur. An inner ear infection causes a condition known as labyrinthitis, which is the swelling and irritation of the inner ear. Such an ear infection causes symptoms such as vertigo, dizziness, hearing loss, nausea or vomiting, and tinnitus.

Viruses are the most common causes of ear infections in the inner ear, although bacteria can be what causes an ear infection if a bacterial infection in the middle ear spreads to the inner ear. Inner ear infection causes include:

  • Cold or Flu viruses – The most common causes of ear infections in the inner ear are cold and flu viruses. They can spread from the respiratory system into the middle ear and then into the inner ear.
  • Other viruses – There are less common viral causes of ear infections including measles, herpes, mumps, and glandular fever.
  • Complications of a middle ear infection – A middle ear infection can spread into the inner ear. This is the most common cause for a bacterial infection in the inner ear.
  • Ear damage after a head injury – Injury to the ear or head can expose the inside of your body to unwanted bacteria.


When to Contact a Doctor

If you think you are experiencing ear infection symptoms, and the symptoms last longer than one or two days, you should consult with a doctor. Sometimes ear infections do resolve on their own after a couple of days, but if the pain worsens or lingers, you should seek medical attention. Additionally, if you have fluid draining from your ear or your hearing is impaired by any of the symptoms of ear infections, you should see a doctor as soon as possible. If you think you have symptoms of labyrinthitis (inner ear) then it is best to contact a doctor right away.

If properly treated, ear infections will not lead to any other complications. If left untreated your ear infection can, in rare cases, pose more serious health issues, including:

  • Mastoiditis – a rare inflammation of a bone that is adjacent to the ear
  • Hearing loss
  • Eardrum perforation
  • Facial nerve paralysis
  • Meniere's disease – a disease that manifests as symptoms of vertigo, hearing loss, pressure in the ears and ringing in the ears.

Letting an ear infection go on without treatment can lead to permanent hearing loss and possible spread of the infection to other parts of your head. If you suspect you might have an ear infection, consult with your doctor or visit an urgent care center to get treatment as soon as possible.

Read more from our Ear Infection Series:

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Ryan Quinn

Ryan Quinn

Ryan has a background in geochemical research and enjoys writing on technical subjects like health and science. He lives in Salt Lake City, UT and can be found recreating in the local mountains.

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