Q. I have recurrent ear congestion. What causes it? How can I treat it?

A. The middle ear contains air. This air is normally able to enter and exit through the eustachian tube. This is a small canal between the middle ear and the back of the nose.

The eustachian tube should have free passage of air. But when this tube becomes inflamed, it can swell shut. This can happen when there is an allergy or a virus infection that creates congestion in the nose.

Sometimes, the eustachian tube can be “sucked” closed, when there is a rapid change in pressure. This is more common during air travel. Young children are more likely to have the eustachian tubes close than adults.

If the eustachian tube is closed, air behind the eardrum is gradually replaced by fluid. This fluid does not drain easily and it can stay for a while.

Congestion in the ear may involve infection, called “otitis media.” Or, the fluid may be sterile. In this case, the congestion is named “serous otitis.” Either way, congestion in the ear can cause pain, temporary loss of hearing and clicking noises with a feeling of fullness in the ear.

Treatments for ear congestion can include decongestants and allergy medicine. If the cause is a bacterial ear infection, doctors usually prescribe an antibiotic. However, most ear infections are caused by viruses that are not killed by antibiotics.

Letting time pass helps, too. Symptoms can persist for weeks, but the eustachian tube almost always reopens on its own.

Dr. Mary Pickett is an associate professor of medicine at Oregon Health and Science University and Harvard Medical School lecturer.