Fluid may accumulate in the middle ear, and become infected from bacteria or viruses which reside in the back of the nose or the throat. The middle ear is connected to the nose and throat by the eustachian tube, one on each side. This muscular tube is immature in both its size and orientation in young children. As they grow, the tube changes direction from a horizontal angle to more of an acute angle, allowing for better drainage and pressure equalization in the middle ear. Children may also have enlarged adenoids contributing to recurrent ear infections.
Adenoids are a mass of lymphoid tissue that sit behind the nose.
If they are enlarged, they may block the ability of the eustachian tube, which extends from the middle ear to the adenoid region, to allow fluid drainage from the middle ear. Bacteria may also remain in the adenoid region, and may further lead to risk of recurrent ear infections. There are certain 'risk factors' which have been shown to put a child at increased likelihood of having recurrent ear infections. For infants, taking the bottle to bed at night may result in bottle feeding 'refluxing' into the back of the nose, and even eustachian tubes. Breast feeding is associated with a lower incidence of recurrent ear infections in infants.