What Causes Ear Infections?

doctor examining an ear

Story at-a-glance -

  • Ear infections can be linked to various causes. The type of ear infection that a person may be diagnosed with can show hints of what ultimately caused the disease
  • There are also common activities that may predispose a person to ear infections. Swimming, or even bathing or showering too frequently may lead to outer ear infections, since water that might be left inside the ear canal may serve as a breeding ground for bacteria or fungi

Ear infections can be linked to various causes. The type of ear infection you’re diagnosed with can show hints of what ultimately caused the disease.

Bacteria and Viruses Mainly Trigger Ear Infections

Some bacteria strains are considered primary causes of middle ear infections. Such strains include:1

  • Streptococcus pneumoniae, S. pneumoniae or pneumococcus — This bacteria strain triggers 40 to 80 percent of middle ear infections in the U.S., making it the most common bacterial cause of middle ear infections.
  • Haemophilus influenza — The next most common culprit of ear infections, the Haemophilus influenza bacteria accounts for 20 to 30 percent of acute infections.
  • Moraxella catarrhalis — This strain triggers around 10 to 20 percent of ear infections.

The Streptococcus pyogenes and Staphylococcus aureus strains may trigger ear infections too, although cases are rare.

Ear infections may also be caused by viruses, with some paving the way for a bacterial infection. The rhinovirus, which is often responsible for colds, is said to have a major role in the development of ear infections. However, take note that the rhinovirus doesn’t directly cause an ear infection.

The rhinovirus’ effect takes place when you or someone you know has a cold. This virus can cause swelling in membranes along the walls of the body's inner passages and disruption of proper airway function. Should inflammation reach the Eustachian tube connecting the throat to the middle ear,2 this may cause a failure of the middle ear to properly drain. Afterward, fluid builds up and serves as a breeding ground for bacteria and infections. Other viruses that may trigger ear infections include:3,4

  • Respiratory syncytial virus (RSV), which is often responsible for childhood respiratory infections
  • Influenza (flu)
  • Herpes viruses
  • Epstein-Barr virus
  • Polio

How Do Medical or Physical Conditions Lead to Ear Infections?

Some medical or physical conditions may cause ear infections, since they can lessen the ear’s defensive system and raise a person’s infection risk. For example, children whose Eustachian tubes are shorter than normal and are relatively horizontal have a higher ear infection risk.5

A middle ear infection can also be caused by an abnormal or malfunctioning Eustachian tube. This causes negative pressure to build up in the middle ear and trigger fluid to leak in through the capillaries. A faulty Eustachian tube can cause otitis media with effusion (OME), or the presence of a thick or sticky fluid behind the eardrum in the middle ear,6 to develop after a middle ear infection. People with the following health disorders may be predisposed to ear infections too:7

  • Congenital structural abnormalities like cleft palate
  • Genetic conditions such as Kartagener’s syndrome, wherein the cilia (hair-like structures) in the ear become immobile and lead to a fluid buildup
  • Down syndrome or fetal alcohol syndrome because of anatomical abnormalities

Fungal Infections May Cause Outer Ear Infections

Otomycosis, or a fungal infection that develops on the outer part of the ear,8 is typically caused by Candida and Aspergillus.9 In some cases, bacteria strains may combine with fungi and complicate the situation.

Fungal ear infections are more common in tropical and warm regions, since fungi grow better in these environments.10 It’s also worth noting that this type of ear infection is more common during warm summer months,11 where fungi can find moisture and warmth that they need in order to grow.12

The risk for a fungal ear infection increases greatly among swimmers, regardless of whether they swim in clean or contaminated water.13 A higher risk for outer ear infections can occur among people with diabetes mellitus, ear trauma or injuries, and eczema or other chronic skin problems.14

These Common Activities May Lead to Ear Infections

There are common activities that may predispose a person to ear infections. Swimming, or even bathing or showering too frequently15 may lead to outer ear infections, since water that might be left inside the ear canal may serve as a breeding ground for bacteria.16

An injury to the thin layer of skin lining the ear canal, whether caused by intense scratching, using headphones, rubbing cotton swabs in the ear, or by allergies caused by either hair products or jewelry, may damage the skin, promote bacterial growth and raise ear infection risk. Lastly, constant moisture may reduce your ears’ supply of cerumen or earwax, which is considered the ears’ natural defense against infections, and eventually lead to an infection.17

MORE ABOUT EAR INFECTION

Ear Infection: An Introduction

What Is an Ear Infection?

Ear Infection Symptoms

Ear Infection Causes

Types of Ear Infection

Ear Infection in Babies and Children

Are Ear Infections Contagious?

Ear Infection Treatment

Essential Oils for Ear Infection

Ear Infection Prevention

Ear Infection FAQ

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