An ear infection is caused by an accumulation of fluid and bacteria in the middle ear, which come from the narrow passageway connecting the ear to the throat called the Eustachian tube. Normally this tube protects the middle ear from mucus and germs in the back of the nose.  Young children, however, have a short, floppy, and horizontal tube that reduces this protection, which can lead to ear infections if germs travel up the tube and reach the middle ear. Drinking while lying down can also have the same effect. Children 2 years old and younger are the most likely to suffer ear infections due to a shorter and more horizontal Eustachian tube and weaker immune system.  The risk tends begins to subside gradually after age 4.