Otitis media with effusion (OME) is fluid in the middle ear space without symptoms of an acute ear infection. Unlike children with an acute ear infection, children with OME do not act sick.

Almost every acute ear infection is followed by days or weeks of OME. In addition, many people develop OME without first having acute inflammation.

OME occurs when the Eustachian tube, which connects the inside of the ear to the back of the throat, becomes blocked. This tube helps drain fluids to prevent them from building up in the ear. The fluids drain from the tube and are swallowed.

When the Eustachian tube is partially blocked, fluid builds up in the middle ear. Bacteria that are already inside the ear become trapped and begin to multiply.

The following can cause swelling of the lining of the Eustachian tube, leading to increased fluid:

• Allergies
• Irritants (especially cigarette smoke)
• Respiratory infections

The following can cause the Eustachian tube to close or become blocked:

• Drinking while lying on your back
• Sudden increases in air pressure (such as descending in an airplane or on a mountain road)

Although many things can lead to a blocked tube, getting water in a baby's ears will not.

OME is most common in winter or early spring, but can occur at any time of year. It can affect people of any age, although it occurs most often in children under age 2. (It is rare in newborns.)

Younger children get OME more often than older children or adults for several reasons:

• The tube is shorter, more horizontal, and straighter, making it easier for bacteria to enter.
• The tube is floppier, with a tinier opening that's easy to block.
• Young children get more colds because it takes time for the immune system to be able to recognize and ward off cold viruses.

The fluid in OME is often thin and watery. It used to be thought that the longer the fluid was present, the thicker it became. ("Glue ear" is a common name given to OME with thick fluid.) However, it is now believed that the thickness of the fluid has more to do with the particular ear than with how long the fluid is present.