Ear Infections | Causes & Risk Factors


What causes otitis media with effusion?

Fluid may build up in the middle ear for several reasons. When a child has a cold, the middle ear may produce fluid just like the nose does. A tube called the eustachian (say: "you-stay-shun") connects the middle ear with the back of the nose. Normally, the eustachian tube lets fluid drain out of the middle ear. However, bacteria or viruses can infect the lining of your child’s eustachian tube causing it to swell. The adenoids (glands near the ear) can also become enlarged and block the eustachian tubes. It is also not a good idea to let your baby fall asleep with a bottle or to leave a bottle in the crib. Drinking while lying down may also block the eustachian tubes.

If the eustachian tubes are blocked, fluid in the ear cannot drain normally. If bacteria grow in the middle ear fluid, an effusion can become a middle ear infection (acute otitis). This will usually increase pressure behind the eardrum and cause a lot of pain. The eardrum will become red and bulging. If this happens, your child may need to be treated with antibiotics.

Children who have frequent ear infections can also develop otitis media with effusion after their infection is gone if the fluid stays in the middle ear.

Children may be at higher risk for ear infections if they:

  • Are around people who smoke.
  • Have had previous ear infections.
  • Have a family history of ear infections.
  • Attend day care (because they are exposed to more germs and viruses).
  • Were born prematurely or with a low birth weight.
  • Have frequent colds or other infections.
  • Take a bottle to bed.
  • Use a pacifier.
  • Are male (boys tend to get more ear infections than girls).
  • Have nasal speech (caused by large adenoids that block the eustachian tube).
  • Have allergies with nasal congestion.

What causes swimmer's ear?

Several things can make swimmer's ear more likely, including the following:

  • If you swim or shower a lot, too much water can get into your ears. Water removes the protective ear wax, which makes it easier for germs and fungus to grow.
  • Cleaning your ears can remove the protective wax layer and lead to infection.
  • If you injure the skin in the ear canal by putting your finger or some object (such as a cotton swab or a pencil) in your ear, an infection can develop in the canal.
  • Skin conditions (such as psoriasis) that occur in other parts of the body can also occur in the ear canal and cause an infection.
  • Bacteria from products you use in your hair (such as hairspray or hair dye) can get trapped in the ear canal and cause an infection.


See a list of resources used in the development of this information.

Written by familydoctor.org editorial staff

Reviewed/Updated: 07/13
Created: 01/99