Ear infection, inner - Causes of middle ear infections

Most middle ear infections (otitis media) are caused by a viral or bacterial infection spreading into the middle ear.

They often occur when an infection, such as a cold, leads to a build-up of mucus in the middle ear and causes part of the ear called the Eustachian tube to become swollen or blocked.

The Eustachian tube is a thin tube that runs from the middle ear to the back of the nose. Its main functions are to help maintain normal air pressure within the ear and to help drain away mucus and other debris from the middle ear.

If the tube becomes swollen or blocked, mucus can't drain away properly, which makes it easier for an infection to spread into the middle ear.

An enlarged adenoid (soft tissue at the back of the throat) can also block the Eustachian tube, which can cause a build-up of mucus and lead to a middle ear infection. The adenoid can be removed if it causes persistent or frequent ear infections. Read more about removing adenoids.

Who's most at risk?

As a child's Eustachian tubes are smaller than an adult's, they are more likely to become blocked and infected. A child's adenoids are also much larger than an adult's in relative terms.

These are the main reasons why more than 75% of middle ear infections occur in children younger than 10, with most cases affecting infants between 6 and 15 months old.

Other factors that can increase the risk of developing a middle ear infection include:

attending a nursery or day care centre – this increases the chances of a child being exposed to infections from other children
being exposed to tobacco smoke (passive smoking)
being fed formula milk, rather than breast milk
having a family history of middle ear infections
feeding your child while they are lying flat on their back
using a dummy
having a cleft palate – a type of birth defect where a child has a split in the roof of their mouth
having Down's syndrome – a genetic condition that typically causes some level of learning disability and a characteristic range of physical features

Glossary

Tissue: Body tissue is made up of groups of cells that perform a specific job, such as protecting the body against infection, producing movement or storing fat.
Immune system: The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.
Bacteria: Bacteria are tiny, single-celled organisms that live in the body. Some cause illness and disease and others are good for you.
Chronic: Chronic usually means a condition that continues for a long time or keeps coming back.