A tube called the eustachian (say: "you-stay-shun") tube connects the middle ear with the back of the nose. Normally this tube lets fluid drain out of the middle ear. If bacteria or viruses infect the lining of your child’s eustachian tube, the tube gets swollen and fills with thick mucus. This keeps fluid in the ear from draining normally. Bacteria can grow in the fluid, increasing pressure behind the eardrum and causing pain.
The eustachian tubes can become blocked because of allergies, or a cold or other infection. In other cases, the adenoids (glands near the ear) become enlarged and block the eustachian tubes.
Acute ear infections usually clear up within 1 or 2 weeks. Sometimes, ear infections last longer and become chronic. After an infection, fluid may stay in the middle ear. This may lead to more infections and hearing loss.