Otitis media often begins when infections that cause sore throats, colds, or other respiratory or breathing problems spread to the middle ear.

But this illness can also affect adults. Children are more likely to get a middle ear infection because their immune system is still developing. A child's eustachian tubes are shorter and straighter than in an adult.

The eustachian tube is usually closed. But it opens regularly to allow air into the middle ear. This tube also equalizes air pressure in the middle ear. A eustachian tube that is blocked by swelling of its lining or plugged with mucus from a cold or for some other reason can't open. The lack of fresh air may allow fluid from the tissue that lines the middle ear to collect. If the eustachian tube stays plugged, the fluid can't drain and begins to collect in the normally air-filled middle ear.

The adenoids in children are larger than they are in adults. Adenoids are made up mostly of cells (lymphocytes) that help fight infections. They are at the back of the nose, near the eustachian tubes. Enlarged adenoids can keep the eustachian tube from opening. In addition, adenoids may themselves become infected. This infection may spread into the eustachian tubes.

Other symptoms include unusual irritability, tugging or pulling at one or both ears, fever, and fluid draining from the ear. The child may not respond to quiet sounds.

Also, children who attend day care are more likely to develop the illness. And babies who are given a bottle while they lie down are also at risk.