Ear infections are super common in kids: Nearly 75 percent of children will have at least one ear infection by age 3, according to the National Institute on Deafness and Other Communication Disorders. (Of this group, about half of children will have up to three ear infections by that age.)
Ear infections occur when the eustachian tubes (tubes near the eardrum that connect the ear to the back of the throat) become blocked and can't drain fluid properly, says Amelia Drake, MD, professor of pediatric otolaryngology at the University of North Carolina, Chapel Hill, School of Medicine. Fluid trapped in these tubes can become a breeding ground for bacteria, resulting in redness and inflammation of the eardrum, and a generally harmless but painful infection.
Ear infections typically follow colds or allergy symptoms like a stuffy nose because these conditions make fluid more likely to collect and get trapped in the ear. Children under 3 are more susceptible to ear infections than older kids or adults because their immune systems are still developing (so they get sick more often) and their eustachian tubes are still growing, says John McClay, MD, a pediatric otolaryngologist at Children's Medical Center Dallas in Texas. At this age, a child's eustachian tubes are short (about 1/2 inch) and horizontal, but by the time kids are 5 or 6, their tubes are three times as long and are positioned more vertically, which helps fluid drain more easily and prevents infection.
Additionally, the location and size of children's adenoids -- infection-fighting immune system cells in the back of the throat -- make toddlers especially prone to ear infections. "Between 18 months and 2 years, a child's adenoids are enlarged because they have been processing bacteria to help develop the immune system. Large adenoids are often chronically infected and, because of their location next to the eustachian tubes, can easily spread bacteria to the ear," says McClay.