An ear infection, also called otitis media, is specifically an infection of the middle ear, the part that contains tiny bones that transmit sound from the eardrum to the inner ear. The middle ear produces secretions, which normally drain to the back of the throat through the eustachian tubes. However, if the fluid doesn't drain and builds up in the middle ear, it creates a warm, moist environment where germs love to grow. Invading bacteria or viruses thrive and result in the pain, crankiness, and fever that signal to parents that their child has developed an ear infection.
Ear infections are not always easy for parents to diagnose, because the symptoms can be vague and mimic those of a regular cold or flu. In fact, ear infections often start as a cold with a cough and a runny nose. A cold virus causes the entrance to the eustachian tubes to swell, so it's easier for fluid to get trapped in the middle ear and infected. The next thing you know, your baby has a fever and is getting very irritable. He may also pull on his ears and seem crankier when lying down, because this position causes the fluid to push on the eardrum, resulting in more discomfort.
The only way to be sure that your child has an ear infection is to visit your pediatrician. Take a baby younger than age 2 to the doctor if a cold and apparent discomfort don't go away in two or three days, or if a fever doesn't go away in one or two days. (If your infant is younger than 4 months, notify your doctor of any fever immediately.) When your physician peeks into your child's ear to check for signs of an infection, she's looking at the eardrum to see if it is red, thick, or bulging.