How can an infection in the throat or nose lead to a middle ear infection?

A tube named eustachian tube connects the middle ear with the nasal pa*sages and the throat. It helps balance air pressure in the middle ear with that in the environment. In older children and adults, the tube is relatively vertical, wide, and rigid, and secretions that pa*s into it from the nasal pa*sages drain easily. In infants and younger children, the eustachian tube is more horizontal, narrower, less rigid, and shorter. Thus, the tube is more likely to become blocked by secretions and to collapse, trapping the secretions in or close to the middle ear and preventing ventilation of the middle ear (that is, blocking air from reaching it). Also, the secretions may contain viruses or bacteria, which multiply and cause infection. Or viruses and bacteria can move back up the short eustachian tube of infants, causing middle ear infections.

At about the age of 6 months, infants become more susceptible to infection because they lose protection from their mother’s antibodies, which they received through the placenta before birth. Breastfeeding appears to partially protect children from ear infections because breast milk contains the mother’s antibodies.